Though WWE has not yet made the John Cena vs. Undertaker match official, it has been planned for months and The Undertaker has been training for a match, according to the Wrestling Observer Newsletter.
The Undertaker will definitely be at WrestleMania. Vince McMahon reportedly felt that everyone already assumes that The Undertaker will be there and officially announcing the match probably won’t get any new people to sign up for the WWE Network. The “mystery” behind the angle and seeing what the payoff will be will probably generate more interest than announcing a straight up match ahead of time.
However, there has also been some talk that there is a chance that we may not see an actual match and instead may just see some sort of “confrontation” between Undertaker and Cena, which could potentially lead to a match later… possibly even at next year’s WrestleMania. The original idea when it was first planned months ago was that it would be a match, though.