Cain has as good of a chance at beating Fedor as anyone else.
The fact is, it's been 10 years, and over this course there have been countless "X guy can beat/is ready to fight Fedor", and it always ends the same way.
That's not to say these threads are old, Fedor is just a man and can be beaten, just very unlikely.
I would see Fedor KO/TKO cain in the first or second, as I believe Fedor will overwhelm him as quickly as possible to avoid the clinch with a wrestler in a cage (he would do this with Randy, Brock, and Carwin as well). I believe he'd put the pressure on and use that power and speed of his to drop and put Cain away. I'd see Fedor simply working faster, harder, and trying to finish the fight earlier, because of the style matchup, and I believe he would, indeed, finish it early (first or second, as stated).
Also, yes, I know Cain's striking is improving, but it's not on Fedor's level, it isn't.