According to Dave Meltzer, John Cena vs. AJ Styles for the WWE Championship is not the plan for this year's WrestleMania as the company actually has something much bigger in mind for the leader of the Cenation. Apparently, his opponent at the Showcase of the Immortals will be made clear at the upcoming 25th anniversary show for RAW which isn't a surprise given how big that will be.
In fact, the plan is for a number of angles for top WrestleMania matches to be set up on RAW that night (January 22nd) and speculation still points to Cena ultimately doing battle with The Undertaker.
Bryan Alvarez theorises that The Deadman will tease his retirement on this edition of RAW and that will lead to Cena interrupting him and challenging the WWE legend to one final match at WrestleMania. That's the bout fans wanted to see last year and Alvarez adds that there are huge plans in place for Cena at the event which is bigger than any of the title match scheduled to be on the card.