Honestly Punk/Edge would be the epitome of awesome Mania Main events. But honestly, I see any possibility of Jericho,Punk,Taker,Orton or Sheamus as his Mania match, we all have to take into consideration that he was the one to win the Royal Rumble match. I am one who doesn't want to see any sort of multi-man Mania match (but Punk/Jericho/Edge would be the ultimate Mania match imo)
Jericho isn't likely to win the WHC/WWE title but how likely was Edge coming back and winning the RR? So never say never especially in the WWE.
Punk who is imo the most deserving of a big time Mania match is a good choice also, but working in the WHC/WWE title would be a factor; but being that he is likely to be in the EC match for the WHC he could by all means win.
Undertaker is another possible opponent, but being that it seems as if the WWE wants to get Edge over as a face having him face The Undertaker would be the ultimate act of booking suicide. The fans love Taker, especially at Mania, besides Edge has already faced Taker at Wrestlemania (and imo had a terrible match) I have a feeling that he is going to drop the Strap before Mania anyway. His best Wrestlemania matches are always imo not for a title, but merely to add to the streak (HBK,Orton, the 1st Kane match etc.)
Sheamus, Please. Sheamus is hardly considered a credible champion and honestly I do not know if he will even be champion come Mania tbh. He hasn't done anything to warrent any credibility imo and Edge winning would do nothing but hurt Sheamus' monster push imo.
That leaves Randy Orton. Orton/Edge I think could have a good match, but with the way the WWE (either purposely or inadvertantly) had made Orton look like a face at RR and Edge, with his face turn could cause a clashing fan reaction. But of the people I have mentioned he is the strongest candidate for a title match with Edge.