Wrestlemania rematch - Traditional 1 vs 1 match
Undertaker vs John Cena

The Undertaker will wrestle at Summerslam. That is confirmed. He will have a rematch at Summerslam. That is also confirmed. Who will he face? No idea.
Ever since The Undertaker was called out at Wrestlemania 34 by John Cena, he has increased his appearances at wrestling events and has wrestled a lot. He is also in a much better shape than he was a year prior to his return, i.e. Wrestlemania 33. Now, the question is, who will he face?
Undoubtedly, his Summerslam bout will be a rematch of one of his recent matches. So, let's count the possible opponents one by one. Triple H - Nope, he will face him at MSG later this year. Brock Lesnar? He is already booked as the Universal Champion. Bray Wyatt? Not a chance. He is quite below the Undertaker's level at this point. Shane McMahon? Probably, but I don't think WWE will want a rematch of their underwhelming match of Wrestlemania 32. Roman Reigns? Involved in the Universal title picture. Also, WWE wouldn't want him to get booed once again. Rusev? Nah. That only leaves Cena. Thus, my prediction is : Cena vs Undertaker for a Wrestlemania rematch.
I don't believe that the Undertaker will lose against Cena. He needs every bit of momentum he can get following his disappointing loss against Reigns at Wrestlemania 33. Also, it will continue the 'Cena losing' story-line that could have greater implications.
Winner: The Undertaker
Match predictions: Will be a bout mostly for the nostalgia, as both of the wrestlers are past their prime.