It'd be interesting to see what Brock could do. Nobody can stop Brock's takedowns so if he wanted Fedor on his back, he'd get it done (they showed a stat prior to the Couture fight - out of every 6 attempts, he's only stopped 1 time - that's awesome!). How is Fedor's guard? I haven't seen him on his back ever, but I've only seen him fight a few times and never was he in any danger. I just think that Brock could pose some problems to Fedor with his size and wrestling ability.
I'd still give the win to Fedor, I see maybe a KO with his striking or maybe a submission using his sambo skills, but I don't think he'd roll through Brock by any means.