#4 Kevin Owens
Kevin Owens never got his rematch after losing the Universal Championship to Goldberg at Fastlane before WrestleMania 33. It is understandable to argue that Owens shouldn't face Lesnar because he's a heel and a heel vs. heel dynamic often doesn't work, but there is plenty of time to transition Owens into a role where he plays a quasi-heel or reluctant anti-hero.
Owens has the in-ring skills to have a great match with Lesnar and the promos he cuts against Paul Heyman would be electric. However, Owens in his current avatar cannot be seen as a threat to Lesnar. Moving him away from the traditional cowardly, dastardly heel character would be a good move.
Owens was fantastic as 'The Prizefighter' when he first debuted on the main roster against John Cena and a return to that character would help build him up to be a credible threat to Lesnar.