John Cena vs. The Undertaker is still the plan for WrestleMania right now, according to the Wrestling Observer Newsletter.
On Raw, John Cena cut a promo saying that a match with the Undertaker was “impossible” and wouldn’t be happening. This was done specifically to “throw people off the scent” for a few weeks, according to Dave Meltzer. Cena will be wrestling for the WWE Championship at Fastlane, and right now the plan is to start the program with the Undertaker after that.
According to Meltzer, the “only way that would change” would be if The Undertaker gets hurt while training or if he decides to pull out for some other reason, which right now seems unlikely.
There were rumors earlier in the week that Rey Mysterio would be wrestling Cena at WrestleMania, but those are unfounded right now according to all reputable sources. Mysterio will be meeting with Triple H to discuss a deal very soon, though, so there is a chance that we will see Mysterio in WWE this year.