#6 Rey Mysterio
Let's get this one out early. A surprising report from Justin Barrasso of Sports Illustrated suggests Rey Mysterio will face John Cena at WrestleMania. Some reports had also stated that he was backstage in the Staples Center and was working on a deal with the WWE.
In many interviews, the luchador has stated that he is open to work with the WWE, evident by his return at the Royal Rumble, but in a part-time schedule. His entry at 2018 Royal Rumble had accumulated 13 million views on YouTube - more than Ronda Rousey's appearance, which garnered only 3 million views.
This match won't have a good storyline other than Cena's desperation to have a match at WrestleMania and going to any length to have it. The fact that Mysterio has challenged Justin "Thunder" Liger to a match at Strong Style Evolved will do more bad than good for the WWE. This is a dream match which we can see perhaps at next year's WrestleMania, but maybe not this year.