#4 Baron Corbin
Baron Corbin is one of the most logical choices to face Seth Rollins after retiring the legendary Kurt Angle at WrestleMania. He is riding high on heel heat at the moment, as no one wanted him to be the last opponent for Kurt Angle. He didn't just face Angle on his retirement match but he pinned him clean too.
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Corbin would surely remind people of his win over and over again, which would give fans more reasons to hate him, setting him up to put over Seth Rollins as a huge face who will finally shut Corbin up with a Stomp.
#3 Rey Mysterio

Rey Mysterio has little-to-no momentum at the moment, after his squash loss at WrestleMania and then a botch at RAW followed by a brutal beatdown at the hands of Lars Sullivan.
Although, Mysterio is a legend in the business and always has a mystique attached to him which makes him suitable for any situation irrespective of his momentum.
Rey is on the last legs of his career and is in WWE to put over young talent. A win over a legend would give Rollins title reign a significant boost.