Personally I think a high profile match involving AJ Lee would be a great choice, having her face Trish Status would make sense to. Truth be told, since the likes of Trish Stratus, Lita and say Stephanie McMahon there hasn't really been a female in WWE that has made the impact AJ Lee has made over the last year. I think if they picked Trish Stratus they could easily make it a believable match with a solid storyline.
Triple Threat Match? I honestly have no desire to see these three in a triple threat match, Undertaker is WAY past his prime and can barely stand these days, Shawn Michaels is retired and should stay as such. Triple H is the only one of the three that I could see in a match for Mania but the question is against who? Now whomever they were to pick, I would make the match against someone that could obviously gain momentum by beating someone of Triple H's status. If Dolph Ziggler wasn't in the World title picture at Wrestlemania, I think he could be the most obvious choice as someone to go over Triple H at Wrestlemania, that or Damien Sandow. Now both of those would be dream matches to me for Mania, Triple H vs. Dolph Ziggler or Damien Sandow.
John Cena/Ryback.. Honestly like said above, a match like this is something that is barely worthy of main eventing Raw. But whether we like it or not, Ryback is going to be in a high profile feud going into Wrestlemania. I like John Cena, he isn't the most sound in the ring but I think this would be the best option for him if they went ahead with this idea for a feud/match. I really have no desire to see Rock/Cena again so having Ryback going up against John Cena on the biggest stage of all would help cement Ryback as a top dog in WWE. That being said, this would be no dream match for me whatsoever but it would makes sense and keep both of these guys busy at Mania and allow the talented guys to be in bigger and better matches.
CM Punk/Brock Lesnar would and could work very well, if they decide to not go with Steve Austin/CM Punk then I think given current storylines having Punk going up against Lesnar would work perfect. CM Punk and Brock Lesnar could be involved with Paul Heyman over the next several months eventually leading up to a rift in the ranks having them both vie for the top spot with Paul Heyman by their side. The match could be for managerial purposes and even the WWE Title.
My favorite out of all five mentioned would have to be Rock N' Sock Connection vs. Team Hell No. I think this would be a great high profile tag match and would work fine for Mick Foley considering it would be a tag match. Given the fact that the Rock "rock bottomed" Daniel Bryan before, they could make this work just fine. Would really be a great idea and have someone like Daniel Bryan getting a rub from three of the biggest from the attitude era and if WWE wants to hype the attitude era due to the new WWE 13, this would make the most sense. All this being said, I don't know if they'll still have Kane and Daniel Bryan wrestling in a tag team by then, but if this is true then I say they should pounce on this idea. You could easily have Kane or Daniel Bryan costing the Rock the WWE Title at Wrestlemania leading up to a tag match between the four.
I've got a few dream matches myself which I may or not post, but these are my thoughts on the five mentioned anyways.