A lot of the reason that Cena and Reigns will happen is down to Vince McMahon. At the end of the day, the WWE is still his toy ring, and his two favourite toys are John Cena and Roman Reigns. McMahon's love for Cena is clear for all to see. He's the colourful giant that's willing to work every hour of his life for WWE. McMahon probably believes that he's the greatest wrestler of all time. Out of all of the greats who've had Vince's ear, none of them have lasted as long as Cena. He has a deep affinity for the guy and will want him to feature as the main event of the biggest WrestleMania of all time. As for Reigns, Vince has had his back for more than a year now. He's got the look and build of a Vince McMahon guy. Vince wants to see him succeed very badly, he's staying course with the vision for him as the man.