#3 Bobby Lashley
Roman Reigns and Bobby Lashley are currently at 1-1 in terms of victories over one another, so a rubber match between the two men somewhere down the line makes a lot of sense.
Lashley picked up a victory over Reigns in an impressive outing at Extreme Rules, and the two men would go on to top that bout with a great number 1 contendership match on Raw two weeks later, which Reigns obviously won.
As of right now, Bobby Lashley doesn't have any clear program in place. He has entered into a mini-feud with Elias, but that doesn't look as though it will go on any longer than SummerSlam. Vince McMahon has a penchant for big-men matches and pitting Reigns against Lashley for the Universal title is almost guaranteed to put a smile on his face.