With a limited time to promote the event, maybe Rock is simply the backup for his cousin Roman Reigns against Triple H and a heel partner. It would only really need The Great One to show up on one RAW as the reveal of the partner and maybe the go home show in New York to give a final push of promotion to the match. With Roman Reigns having been booked pretty poorly for the majority of 2015, his recent realistic attitude has resonated with the fanbase a lot more and teaming with Rock at WrestleMania could be just the rub that the former Shield member needs to cement himself as a top tier babyface in the eyes of the WWE Universe. It would only make sense that Triple H be the lead heel on the other side given his history with both Rock and Roman. In terms of a partner, the star that makes the most sense at this stage would be Sheamus given hes the one who stole Reigns title at Survivor Series and has been feuding with Roman ever since.