I'm asking this because I'm genuinely curious. I have seen all of Cain's fights but only maybe half of Fedor's so I want to know who everyone thinks will win and how.
Cain due to being a new breed and amazing....I'd say 6-7/10 times he takes it 
kawapes - In the cage, Cain easy. In a ring with pride rules its more debatable but Cain still takes it since he's stronger, better cardio, and more technically sound. Fedor is too wildFedor in his prime was far more calculated than wild. He could get an arm or some good g'n'p off a reversal. But Cain has epic cardio as well as good stand up and good wrestling. Elbows would not be fun for fedors paper skin.
I would love to watch it.
I don't like comparing eras. It's pretty much impossible. That said, I think Cain pretty much grinds him down and wins a UD.
I think a well prepared Big Cat and Cain are the only two guys ever to have a shot at prime Fedor.
It's a great fight.
I gotta go with Cain on this one. But Fedor can knock anyone out.
Both fighters are aggressive, both at prime have good cardio, both have great takedown (though Fedor's was more clinch based), and both are extremely resilient. I think Fedor has a speed, striking, and submission advantage and Cain has an advantage in top control and takedowns. I'd give Fedor a slight advantage and probably the win but it would be the most difficult fight of his career.
I could never bet against a prime Fedor. The Fedor from 2003-05 is the best fighter i have ever seen and in my opinion could beat anyone.
Cain's strengths: better technical stand-up, outstanding wrestler, cardio is off the charts.
Fedor's strengths: speed, power, aggressive style, great balance against wrestlers with his Judo.
I favor Cain, as long as Fedor doesn't land a JDS-like bomb.
My username is relevant
Fedor
Anyone that says Cain immediately doesn't really have any idea about the real Fedor. You may have watched his fights in Pride, but you watched them in hindsight - not when they were happening or even a few months afterwards. So looking at Fedor of today, after his 3 losses, I can't blame people for thinking Cain. But for those of us who watched Fedor in his prime, nobody else even comes close. He breaks them all. Would be a helluva battle though between those 2 monsters.
Fedor.
How quickly we forget.
Shogun05 - I could never bet against a prime Fedor. The Fedor from 2003-05 is the best fighter i have ever seen and in my opinion could beat anyone.This.
MMA is a sport of heart and will where anyone can beat anyone.
the only thing Cain has over prime Fedor is reach. Not striking, takedowns, wrestling, subs, game plan, or cardio. Fedor closes distance on everyone in his prime, so its a real no brainer for me.
JEFF3KIDS - the only thing Cain has over prime Fedor is reach. Not striking, takedowns, wrestling, subs, game plan, or cardio. Fedor closes distance on everyone in his prime, so its a real no brainer for me.Fedor has a wrestling advantage?
Wow.
XcessiveZ -JEFF3KIDS - the only thing Cain has over prime Fedor is reach. Not striking, takedowns, wrestling, subs, game plan, or cardio. Fedor closes distance on everyone in his prime, so its a real no brainer for me.Fedor has a wrestling advantage?
Wow.
In MMA yes. Who outwrestled Fedor in his prime? Coleman?
Maybe not wrestling but submission grappling. Cain has pretty killer top control though, the guy is a monster in the guard.
Fedor, if JDS can rock and KO him Prime Fedor would have taken his head off.
No one beats prime Fedor, not even Cain