#3 Aleister Black
Aleister Black ran through the NXT brand during his time there, and although he hasn't exactly had all the momentum in the world on SmackDown Live, he's still an incredibly gifted performer with a great character.
Black carries an aura with him that few in the company can match, and despite the fact that he is quite a bit smaller than Brock Lesnar, he's a fantastic match and the mesh of character would be quite interesting.
Usually, it is Black that intimidates his opponents through his dark and mysterious aura, but Brock is intimidated by no man, so it would be quite enjoyable to see how that plays out. Ultimately, this one is probably the least likely on the list, but given how talented both men are, they could put together an incredible bout that would elevate the Dutch Destroyer to the main event level, as he is a potential future World Champion.