Many theories about who will fight the Admirals but I never have seen anything on John Giant. Sure, he not a Top Tier, but we saw him ordering around other Vice Admirals. He is important. I see two possibilities. Either Luffy or Robin.
1) Oda might try to replay certain Whitebeard moments with Luffy. So Whitebeard easily defeated John Giant. He made a quake and then jumped and hit the Vice Admiral. Luffy could turn the ground under him into rubber to make him shake again and then jump punch too.
2) Saul talked about his dislike for elbafians. Perhaps he got this feeling from his contact with the other gigantic Vice Admirals. John Giant, his former collague, was the first giant of Elbaf to get recruited. I also think that Robin will fight Wolf, so John Giant would be a good enemy before that, to practice fighting big guys. Lastly, John Giant believes in Absolute Justice and Robin is considered the last Devil of Ohara.
1) Oda might try to replay certain Whitebeard moments with Luffy. So Whitebeard easily defeated John Giant. He made a quake and then jumped and hit the Vice Admiral. Luffy could turn the ground under him into rubber to make him shake again and then jump punch too.
2) Saul talked about his dislike for elbafians. Perhaps he got this feeling from his contact with the other gigantic Vice Admirals. John Giant, his former collague, was the first giant of Elbaf to get recruited. I also think that Robin will fight Wolf, so John Giant would be a good enemy before that, to practice fighting big guys. Lastly, John Giant believes in Absolute Justice and Robin is considered the last Devil of Ohara.
