This fight will be a spectacle for sure. Both men weigh over 500+ pounds combined: God only knows what they'll clock in at on fight night.
However, I don't give Carwin more than a punchers chance in winning this. Too many unknown variables surround Carwin's game, mostly concerning his cardio. We've seen Brock go at least three rounds, but none of Carwin's fights have eclipsed five minutes.
Both Carwin and Brock are NCAA collegiate wrestlers, but Brock was Division I while Carwin was Division II. That's a huge gap in talent and quality of opposition. I don't see Brock having much difficulty taking Carwin down to the ground, especially if the fight goes more than one round.
In the UFC, Brock has fought top competition since his debut, and has handled them accordingly. Carwin's biggest test was Gabe Gonzaga, who came close to knocking Carwin out and could've won the fight if not for the errant decision of leaving his chin up during their final stand-up exchange. Credit to Carwin for regaining his senses enough to deliver a counter KO shot, but can he recover from a Brock-type of power shot?
I think people's hatred for Brock clouds their judgment when it comes to picking his fights, thus they'll immediately hop on the bandwagon of his challengers without objectively looking at the match-up. Carwin's got a big right hand - and it can definitely knock a few of Brock's marbles loose - but I can see multiple ways of Brock winning the fight, as opposed to just one for Carwin.