^It needs to be a good match so Hogan (who was generally awful when he was healthy and hasn't gotten any better since he's had repeated hip and knee surgeries) and Austin (who made it very
clear he will never wrestle again as one wrong move could leave him in a wheelchair) are out.
The smart money says Cena. Apart from a brief feud when Cena was a heel, they've never really worked together in a long programme. Whether the more traditional fans like him or not, Cena is the biggest star in wrestling today and as soon as he won his first WWE title, he moved to Raw so they've nearly always been apart. They wrestled on Raw once since but that's about it.
Edit - oh, and he made it 17-0 against Shawn Michaels at Wrestlemania 25 in possibly the match of the decade.