Sheamus (c) vs. Daniel Bryan for the United States Championship: It seems like they're building Sheamus back up so I'd expect him to get a win here, but Bryan getting the title back is also a possibility. This should be one of the best matches of the night, especially if they get enough time, as they have great chemistry. The title change on Raw was fantastic and reports have universally praised their matches at live events, where they've gotten 20 minutes to show their stuff.
The Miz (c) vs. John Cena for the WWE Championship: The real main event is however The Rock gets involved. Would that happen after Cena wins the title to theoretically make the fans happy (though since travelling Wrestlemania fans traditionally don't like him, that might not be the case live)? I'm not sure. Miz winning since he's much fresher as champion, leading to some Cena shenanigans with the Rock, is the most logical situation to me, but I'm really not sure what to expect since the match is just a backdrop for The Rock having a confrontation with Cena.
Edge (c) (with Christian) vs. Alberto Del Rio (with Brodus Clay) for the World Heavyweight Championship: Del Rio will win. It's reportedly been planned for months. He's fresh, and Edge is beyond stale. The seconds at ringside is not the norm for a WrestleMania title match, which makes me expect some sort of chaos leading to the finish, but there's no way Del Rio isn't walking out as champion while personal ring announcer Ricardo Rodriguez comes close to having a heart attack screaming his name.