I think Cruise would beat him because Beiber's ego would get in the way. (not that they don't both have an ego, he just has a bigger one).
Honestly it would take a lot of training for a true fight and Dana White is only looking at the $$$$. I mean, why else would two untrained fighters be a part of the "biggest pay per view". He did the same thing with CM Punk. He knew the pay per view would sell and it did. Punk did train for a long time, but he wasn't ready especially to face the person he did. White just wanted CM Punk's name. Don't get me wrong, I don't dislike White for that; I mean its what he does but its not about the competition, its about the money.