Cena defeats Punk at HIAC. Punk gets Heyman to get Lesnar involved, and gets a rematch at SS. Lesnar finally interferes, and Punk wins the title back.
Leaves TLC - the final Cena/Punk match. TLC-style. End of the saga, final chapter, all that stuff. Hellacious battle, and in the end, Cena wins. Next night, calls it the most grueling four months in his career, and how fitting is it now, he gets The Rock at the Rumble for the WWE Title. Punk, meanwhile, starts to manifest some hate for Lesnar big time for helping him retain, which could lead to Punk/Lesnar at the Rumble - with a little HHH intervention to reset to Mania, perhaps. And they've done heel vs heel at the Rumble before, in case anyone wondered (Orton/Sheamus in 2010, before Orton turned face).
Not sure how to work around the EC yet, but...leaves ya Rock, Taker, Lesnar, HHH, Cena, and Punk as your top 6 for Mania.
Lesnar vs HHH
Taker vs. Cena
Rock vs Punk
Something like that...