Difference between KNOWING and GUESSING
There is indeed a difference. We seem to have this idea that if we say the right answer regardless of how dumb the reason is, then we're right. Not necessarily. What matters the most to be right even if one says the correct answer is the reason behind the answer.
If you say it's going to rain tomorrow because 3 cats crossed the road, and it does happen to rain the following day, you're not exactly correct, you're just lucky because your reasoning was incorrect. It certainly didn't rain because 3 cats crossed the road. If your reasoning for an answer is incorrect, getting the answer correct is simply luck.
What's my point? No one got Kanjuro being the traitor correct, they guessed it. Why do I say that? It's because no one mentioned the reasons the Manga gave for why he was the traitor.
Simply put, if reasoning for an answer is not consistent with the the answer, it's simply luck, not deduction.
No One Could Know It was Kanjuro
Ironically, this is the reality. Why exactly? because there was no evidence or anything substantial to make him out as the culprit definitely.
A List of Insubstantial Reasons People Try to Use
Kanjuro is a Kabuki actor in appearance, therefore he's the traitor: This isn't evidence he's a traitor. We just know that's his design is that of a Kabuki actor. Can't tell Kanjuro is a traitor simply because he's wearing a Kabuki actor. Oda could just as well have said he dresses like one because he has dreams to be an actor. There's not enough detail or context here to use this as reason he's a traitor.
Inuarashi Claiming Jack got to Zou with a Vivre Card: This isn't evidence. Most people knew Jack got to Zou by Vivre card as Inuarashi mentioned it. Problem is we don't know how he got it, therefore, we can't blame anyone.
If this was evidence, Inuarashi would have known who the culprit was, but he never knew. There are so many ways Kaido could have acquired a Vivre card.
How do we know Oden didn't keep Vivre Cards for Zou and he acquired it when he killed him? How do we know the Beast Pirates didn't acquire toe nail clippings of Inuarashi or Nekomamushi, so they could trail them 20 years later?
One point someone made was because Kinemon and Kanjuro knew Raizo went to Zou, therefore, the suspect must be 1 of these 3. That's actually incorrect. How do we know Raizo wasn't the one decided to crash the boat so he could lead the Beast Pirates there? How do we know Kiku wasn't the one who ratted the alliance out?
Kiku was in Wano the entire time Raizo, Kinemon and Kanjuro left for Zou. She would have known they went to Zou, so who is to say she didn't expose their trip to Kaido and Orochi?
Kanjuro was captured by Joker and Escaped: Not a good reason either because Kanjuro was hidden. It's not like he was strolling around nonchalantly with Joker to make him out as a traitor. He actually created a hideout with his ability which would suggest he was actually hiding. Therefore, we couldn't use this to pin him as a traitor.
Birds appearing near Kanjuro: For one, we couldn't really tell if he drew them or not. We had no idea he could draw in the first place.
More so, it's an assumption to claim those birds are even capable of sending messages. We don't know this at all. People are just assuming he can send messages because they've watched Naruto and think of Sai. Would be like looking at Crocodile and saying he can do the things Gaara can do with sand which... he can't. Gaara does things Crocodile could only dream of doing.
In fact, we see Orochi reading the intelligence off paper, not from some bird that Kanjuro drew that landed in his hand. So, it doesn't look like he was sending information with his DF powers as we don't even know if that's possible. We only know he was getting them via paper.
The Reality
As Kinemon said, he can't tell who it is because there was no evidence. The only way he or they (Inuarashi especially) is if they confessed and that's the reality.
Almost every reason we can give for why Kanjuro is the culprit can apply to any of the scabbards which makes it impossible to know if there was a traitor to begin with or who it even was.
Oda created a situation as such that he could literally have made any one of the scabbards the traitor.
He could have said it was Shinobu and we wouldn't be able to say otherwise; he could have said Kinemon or Inuarashi or Nekomamushi or Denjiro (Kyoshiro); there was simply no evidence to cement anyone as a traitor.
Even Orochi said he didn't believe the scabbards were alive.
What does this mean? It means if any of us even said Kanjuro was the traitor, we'd have to say that can't be the case because why then would Orochi say he didn't believe the scabbards were alive IF a scabbard was the one sending him information?
In fact, if people assume Kanjuro sent messages via bird messages. Orochi receiving messages from a magical bird from a DF should be proof Kanjuro (a scabbard) was alive meaning the other scabbards would be alive to.
As Kinemon said, they all nearly died together, so there was literally no way to pinpoint anyone as a traitor.
There was only 1 piece of evidence that there was a traitor, and that was Oda revealing a traitor in the latest chapter. Had Kanjuro not revealed himself, no one would have known for a fact he was the traitor because no one knew the reasons he was a traitor because none of these reasons were given to us in previous chapters.
Furthermore, the fact Oda had to introduce new facts to make him the traitor proves there was no evidence to begin with:
There was no evidence. No one mentioned any of the reasons why he was a traitor because there was none and there was nothing substantial.
There is indeed a difference. We seem to have this idea that if we say the right answer regardless of how dumb the reason is, then we're right. Not necessarily. What matters the most to be right even if one says the correct answer is the reason behind the answer.
If you say it's going to rain tomorrow because 3 cats crossed the road, and it does happen to rain the following day, you're not exactly correct, you're just lucky because your reasoning was incorrect. It certainly didn't rain because 3 cats crossed the road. If your reasoning for an answer is incorrect, getting the answer correct is simply luck.
What's my point? No one got Kanjuro being the traitor correct, they guessed it. Why do I say that? It's because no one mentioned the reasons the Manga gave for why he was the traitor.
Simply put, if reasoning for an answer is not consistent with the the answer, it's simply luck, not deduction.
No One Could Know It was Kanjuro
Ironically, this is the reality. Why exactly? because there was no evidence or anything substantial to make him out as the culprit definitely.
A List of Insubstantial Reasons People Try to Use
Kanjuro is a Kabuki actor in appearance, therefore he's the traitor: This isn't evidence he's a traitor. We just know that's his design is that of a Kabuki actor. Can't tell Kanjuro is a traitor simply because he's wearing a Kabuki actor. Oda could just as well have said he dresses like one because he has dreams to be an actor. There's not enough detail or context here to use this as reason he's a traitor.
Inuarashi Claiming Jack got to Zou with a Vivre Card: This isn't evidence. Most people knew Jack got to Zou by Vivre card as Inuarashi mentioned it. Problem is we don't know how he got it, therefore, we can't blame anyone.
If this was evidence, Inuarashi would have known who the culprit was, but he never knew. There are so many ways Kaido could have acquired a Vivre card.
How do we know Oden didn't keep Vivre Cards for Zou and he acquired it when he killed him? How do we know the Beast Pirates didn't acquire toe nail clippings of Inuarashi or Nekomamushi, so they could trail them 20 years later?
One point someone made was because Kinemon and Kanjuro knew Raizo went to Zou, therefore, the suspect must be 1 of these 3. That's actually incorrect. How do we know Raizo wasn't the one decided to crash the boat so he could lead the Beast Pirates there? How do we know Kiku wasn't the one who ratted the alliance out?
Kiku was in Wano the entire time Raizo, Kinemon and Kanjuro left for Zou. She would have known they went to Zou, so who is to say she didn't expose their trip to Kaido and Orochi?
Kanjuro was captured by Joker and Escaped: Not a good reason either because Kanjuro was hidden. It's not like he was strolling around nonchalantly with Joker to make him out as a traitor. He actually created a hideout with his ability which would suggest he was actually hiding. Therefore, we couldn't use this to pin him as a traitor.
Birds appearing near Kanjuro: For one, we couldn't really tell if he drew them or not. We had no idea he could draw in the first place.
More so, it's an assumption to claim those birds are even capable of sending messages. We don't know this at all. People are just assuming he can send messages because they've watched Naruto and think of Sai. Would be like looking at Crocodile and saying he can do the things Gaara can do with sand which... he can't. Gaara does things Crocodile could only dream of doing.
In fact, we see Orochi reading the intelligence off paper, not from some bird that Kanjuro drew that landed in his hand. So, it doesn't look like he was sending information with his DF powers as we don't even know if that's possible. We only know he was getting them via paper.
The Reality

As Kinemon said, he can't tell who it is because there was no evidence. The only way he or they (Inuarashi especially) is if they confessed and that's the reality.
Almost every reason we can give for why Kanjuro is the culprit can apply to any of the scabbards which makes it impossible to know if there was a traitor to begin with or who it even was.
Oda created a situation as such that he could literally have made any one of the scabbards the traitor.
He could have said it was Shinobu and we wouldn't be able to say otherwise; he could have said Kinemon or Inuarashi or Nekomamushi or Denjiro (Kyoshiro); there was simply no evidence to cement anyone as a traitor.

Even Orochi said he didn't believe the scabbards were alive.
What does this mean? It means if any of us even said Kanjuro was the traitor, we'd have to say that can't be the case because why then would Orochi say he didn't believe the scabbards were alive IF a scabbard was the one sending him information?
In fact, if people assume Kanjuro sent messages via bird messages. Orochi receiving messages from a magical bird from a DF should be proof Kanjuro (a scabbard) was alive meaning the other scabbards would be alive to.

As Kinemon said, they all nearly died together, so there was literally no way to pinpoint anyone as a traitor.

There was only 1 piece of evidence that there was a traitor, and that was Oda revealing a traitor in the latest chapter. Had Kanjuro not revealed himself, no one would have known for a fact he was the traitor because no one knew the reasons he was a traitor because none of these reasons were given to us in previous chapters.
Furthermore, the fact Oda had to introduce new facts to make him the traitor proves there was no evidence to begin with:
- We only just knew he was a Kurozumi - No one could have known this to make him out as a definite traitor.
- He was looking for a place to die from youth - No one could have known this to make him out as a traitor.
- He was a traitor from the beginning - No one could know he was a traitor from the start.
There was no evidence. No one mentioned any of the reasons why he was a traitor because there was none and there was nothing substantial.