At this point, I cannot say.
On one hand, The Miz has been built like crazy over the past month. He's now pwned Cena for four weeks straight, and beaten the hell out of him in the past two. If management wants to cement him as the top heel of the company...THE VILLIAN OF THE WORLD WRESTLING ENTERTAINMENT...then by all means, Miz should win at WrestleMania.
On the other hand, the same reasons Miz could win are the same reasons he may not win. Classic case of Cena "overcoming the odd" so he can send the fans (aka every 5 year old and fat chick in the building) home happy.
What I do know is that if The Rock interferes in the match, even if its to help John Cena, The Miz will retain via DQ.