Brock, first or second round stoppage due to GNP. The real problem with the Mir fight is that his punches, oddly, didn't have enough power and he was trying to hammer fist instead of putting his shoulders and weight into actually punching Mir into paste. I posted after the last fight that is he worked on his hands for a year, which he has pretty much done, he would be unstoppable.
This fight will be interesting, though, for a few reasons. Heath certianly does not have the BJJ that Mir has, but out of his 28 wins, 16 of them have come from submission, so he has a decent ground game. Oddly, he hasn't won a fight by submission in his last eleven fights, and then it was against the great "Khali"

so you can count that or not.
Also, Heath has fought the very best there is, so he isn't likely to be intimidated in any way by Brock. He has fought Fedor, Mirko, Nog (three times!). He's been in the game for eleven years, and he's seen the best the game has to offer, and has fought them. Against the best he has usually lost, but this is the type of experience that will not allow Brock, or his hype, to scare him. To put it in perspective, heath had his first fight in 1997, the same time Brock was trying out for the wrestling team at Bismark State Junior College, Bismark, ND.