Jessica

I doubt Kuzan and Sanji will fight for a few reasons.

One, I think if Kuzan is going to fight a Strawhat it's got to be Robin because of the history there and it would be a good call back to his introduction where she was terrified of him.

Two, I don't think Kuzan is going to make it to the Blackbeard Pirates vs Strawhats match anyway, I'm thoroughly convinced that he (and also Shanks) are going to be killed of by Blackbeard at some point before the final. It doesn't matter if Kuzan is or isn't a spy (to Blackbeard), it just matters what Blackbeards perception of Kuzan is. If Blackbeard is given any reason to doubt Kuzan's loyalty, Kuzan would be on the chopping block. I could also see Blackbeard getting to the One Piece first and just as he's about to get it Kuzan realises that Blackbeard getting his hands on the One Piece isn't going to end well and takes action but he ends up losing.

I could see Sanji maybe having a skirmish with Kuzan if they run into each other but I can't see it being a long drawn out conflict.