According to F4WOnline.com, one WrestleMania 29 match which seems set in stone is Brock Lesnar vs Triple H in a rematch from SummerSlam. As of now, the plan is for Lesnar to return to WWE TV in late February and build up to the PPV bout on April 7th.
At this point, it's unknown whether or not Lesnar will re-sign with WWE after his contract expires following WrestleMania 29. Lesnar signed a one year deal with WWE last year, and it's assumed that the company will offer Lesnar a new deal as officials have been pleased with Lesnar box office numbers and his matches against John Cena and Triple H.
Should Lesnar decide that he doesn't want to work for WWE following his match against Triple H at WrestleMania, the company will once again face a "WrestleMania Hangover" situation, with big name part-timers such as The Rock, Brock Lesnar, The Undertaker and Triple H taking time off.