Regarding next year’s WrestleMania 32, Vince McMahon already has six possible matches in his head for the event. While we don’t know all the specifics yet, Bryan isn’t figured into the plans because there is no telling if or when he’ll ever be able to wrestle again.
In regards to fans wanting to see Sting vs. Undertaker at the event, those plans are also not on the table. Vince is reportedly negative on the idea of the match happening. As far as things stand with WWE, Sting is not yet retired and there are plans for him, so it’s not like WrestleMania was a one-and-done. Sting is also a possibility for the 2016 WWE Hall of Fame.
John Cena’s match is said to be almost a lock, however we don’t know the opponent yet. The featured main event for the show will either be The Rock & Ronda Rousey vs. Triple H & Stephanie McMahon, or two singles, or just The Rock vs. Triple H.
Plans for Brock Lesnar are still up in the air, but his match is also figured in. WWE has been protecting Lesnar ever since Triple H beat him, so Roman Reigns defeating Lesnar would still be the ultimate win to help kick off Reigns as the top superstar on paper.
Source: Wrestling Observer Newsletter
(Keep in mind that things will change, so take this with a grain of salt).