Tbh, I think Beckmann will be a Sanji opponent in the end. If you look all the 1st commanders, they all seem to be tailored to a fighting style we "could" potentially attribute to the crew outside of Marco.
Kata was clearly a Luffy opponent, hence the partial mirror match we got. King is a crazy mix of swordman and whatever the fuck he wants (his body is a weapon lol). Shiryu is another swordsman, and the color spread from 3 weeks ago confirmed that he's BBs number 2, so it makes sense he's a Zoro opponent who will probably have an advantage over King somehow when Zoro gets to him.
But then you have Beckmann, who clearly has used a gun and physical blows with it to take out opponents. He "seems" to have a similar aura as Sanji, maybe it's the cigarette idk. But why I think Beckmann will be Sanji's fight is because I also think Mihawk will partner with Shanks in the EoS, so Zoro will essentially be fighting someone who's much closer in strength to Luffy's opponent (ignoring any Shanks vs Mihawk debates here, I just mean they are much closer in strength than Shanks and Beckmann probably are).
Of course, this is with the assumption that Shanks isn't going to get gimped (which I don't believe) and Luffy will stay true to his words and legitimately fight Shanks and his crew (something I do believe)