I think the consesus tends to be that Takashi is too direct and too stubborn to really be great here, which I agree with. He's very sharp, and would hardly be a walk over, but in a game of guile, rather than force, I don't think he can take the top. Kat, similarly, has a strength that is not applicable directly to poker, as a peace maker and a coalition builder. Yes, she's also a strong woman and not to be under estimated, but it hardly seem to be her style to play that sort of a game, at least for thouse stakes. She is a woman who retired, claiming she would never fight another war.
Of course, if the other three under estimated either Kat or Takashi, and they made a bold move, they could be in it. Neither of them are idiots.
Hanse, Janos and Max are all more protrayed as master manipulators and experts at subterfuge, so seemingly they'd be the three to beat. Personaly, I'd over Max and Janos the edge on their poker faces, since they live in such fear in their daily lives of betrayal by their own families and advisors that they need to learn to keep their feelings to them selves. Max is slipping here, but with out the shock and stress of the war, he might be able to hold on to his sanity long enough for one night of poker. Hanse did show him self a good actor, at Justen's trial and in that affair, but day to day he is with people he trusts and loves like Adrian Sortek and Quintus Allard, so he's got less need to practice that very personal sort of miss direction that Max would tend to thrive on.
I don't think its a slam dunk for anyone. When you look at the House Books, in 3025 every house had a pretty sharp figure at its helm, and I don't think you can count anyone out.