I am very sceptical about this piece of 'news.' The Rock stated only last week he was done with wrestling and he is nowhere near the level he would need to be to work as The Rock again at Mania. What also makes me cast doubts over this report is Michaels' inclusion. It is well documented that Rock hates him and he has also stated he would never wrestle him. So it would take something pretty major for that match to take place.
However, IF Rock has agreed to wrestle one final match at Mania, and gets into peka condition, then it would be an amazing coup for WWE. With all its current problems and fans lack of interest in the industry, it could provide a real shot in the arm. As for his opponenet, at the event, there is one clear favourite: John Cena. For marketability, promo potential and the hype/reaction surrounding that match, nothing else could compare. That is THE BIGGEST match WWE could book for Mania, especially with it being held in Florida.
Other potential candidates are HBK/Orton. Rock/Michaels is a dream match and a match versus Orton could truly establish Orton as a star in WWE and would be a battle of Third-Generation Superstar's. Kennedy/Rock would bomb, imo and MVP is nowhere near ME status to warrant a match with Rocky at Mania.