The out come of the title matches are dependent on each other really...
I personally think they'll go with Del Rio beating Edge, with Christian interfering and turning heel, setting up an Edge/Christian fued. Or even a 3 way thing, but I think that's a bit messy (3 way's normally are, trust me). Then I think in the Miz Cena match, Cena will win clean, no Rock interference and they'll probably celebrate together at the end to close the show.
However if Del Rio wins clean without Christian interference, I still think Cena will win (as people have said, it's doubtful they'll let two heels win in the title matches) then I can see the Rock coming out, shaking Cena's hand etc then Cena giving the Attitude Adjustment to the Rock, instantly turning the new champ heel and really igniting a feud between these two for the next few months, leading to a match at the latest Summerslam. I'm not sure if this will happen of course but I think it would be a great way to set up the rest of the year, and Raw will be a must-see after something like that.
However if Miz wins after interference from the Rock (can't see Miz winning totally clean if he does) this will see the start of a Miz v Morrisson feud, maybe not immediately as I can't see their feud completely ending by Mania, but by about May/June time the former tag team partners will be going at it, and perhaps Miz will put Morrisson over by Summerslam. Infact even if Miz loses at Mania this feud will happen in the near future.
Other matches;
Undertaker - HHH. Taker wins in what will be a great and most violent match WWE has seen in years. I fully expect blood and various tables being broken and weapons used for this one match. WWE has kind of been letting a few Attitude Era type promos slip into Raw recently and even though I don't think this will see a return to that period, I think letting the odd match once or twice a year be that brutal is fine. I can see others coming out and getting involved too, Wade Barrett maybe coming out and attacking HHH or even both of them at some point. Perhaps even Sin Cara? Not sure if he'll get thrown into a fued against those two right away though so maybe not.
If Sin Cara doesn't show up in that match, probably more likely he'll appear in the Cody/Mysterio match. I really hope this is a great match and Cody wrestles out of his skin cos this could spell the start of a big push for him, a return to Raw in the draft, a feud with Daniel Bryan/John Morrison and perhaps even a US/Intercontinental title run in the near future. I think (and hope) Mysterio will lose but this is the result I am actually most unsure about.
Orton V Punk... Punk needs to get put over in this match, he's had a brilliant year and he deserves a WWE title run at some point, and is my outside bet to either win the rumble next year or be going into WM28 as WWE champion. Also expect at least one more PPV match between these two, this grudge won't end at WM, regardless of who wins.
Lawler/Cole... Lawler, clearly. Cole is going to get his ass handed to him. It's the real joke match of the night but this feud and build up has been played out beautifully and I am actually quite excited to see this feud reach it's logical conclusion, no more matches between the two and that would be it.
Big Show and Kane will beat The Corre... The Nexus and Corre stables are on their last legs and if Mania doesn't see the end of these fueds then Extreme Rules will.
I can see the Sheamus v Bryan match ending in a countout or dq or something stupid like that, but hopefully it'll be a great match as I did quite enjoy their Raw encounter. Bryan will go feud Cody or Drew McIntyre, and he is probably quite likely to go to Smackdown in the draft and develop his character a little more and be a much bigger fish. If Sheamus loses the title though I can see him going over to Smackdown and getting into a feud with the Undertaker should he stick around after Mania this time, he normally takes a few months off after Mania but then he's just got back after a big layoff so who knows...
Finally the tag match with Snookie..The faces to go over, Morrisson to continue his fued with Ziggler through to Extreme Rules and after that both get big pushes and title runs this year, wherever they are drafted to (Ziggler is my choice to win his MITB match this year).
Anyway that's my two cents, sorry it was so long!