Unless Rock is unable to work Wrestlemania because of promoting his movie GI Joe, then either Rock-Cena or a triple threat with Punk involved. I think they'll probably do the former, because they would probably prefer the idea of promoting the big one-on-one rematch from last year between Rock and Cena. If Brock-Triple H do end up fighting again (seriously doubt it, and it isn't at all necessary), Punk could make a good opponent for the Undertaker if he isn't put in the main event.