As previously reported, John Cena is rumored to be the opponent for The Undertaker at WrestleMania 33. However, those plans have reportedly not been sealed by Vince McMahon. According to Ringside News, WWE is now also considering having Roman Reigns take on the Deadman at WrestleMania.
The idea behind this is that John Cena is considered a part timer now, and that Roman Reigns facing The Undertaker would have more meaning and impact to his career than Cena. Also, should John Cena and Roman Reigns leave the Royal Rumble PPV as the WWE Champion and Universal Champion respectively, Undertaker would presumably challenge one of them for their title.