Charles gets some good shots in and frustrated Frazier early, but the pressure will eventually catch up to him and he'll start losing rounds and taking more punishment to the body. Frazier by UD, if Charles goes the distance with Maricano, he can go the distance with Frazier.
Boxers struggled mightily with Joe Frazier. Only Muhammad Ali and maybe Larry Holmes could best him in my eyes. Charles was excellent but doesn't make that cut, plus he'd be giving up weight against Joe. Frazier by TKO late.
Frazier was a different type of puncher than Marciano. Not harder but more precise, more accurate inside. Not to mention about 20lbs heavier which can wear down an opponent. Charles was tough but I believe he would get ground down into a fine powder by Joe.
We could also make the argument that if Charles was stopped by Marciano, he would also be stopped by Frazier. Joe was 20 or so lbs heavier, faster on the attack and nearly equal in power. Frazier would steamroll Charles to a late ko/tko.
Logic is a lovely thing, isn't it? This post pretty much ends the thread...unless the OP was referring to the older, softer Frazier from the Foreman fight. Prime for prime, however, this is no contest.
Ezzard Charles is being sold short in this thread. He was an accomplished fighter at heavyweight, and he looked pretty strong and solid at around 185 - 195 pounds. He was a lot better and more durable than Bob Foster at HW. He was HW champion of the world ! And, yes, Frazier beat Ali, who was in 1971 still better - and bigger - than Charles I guess, but I can't see Ezzard Charles being an open target for that left hook over and over like Ali was in 1971. I reckon it would be a tough fight. I'd give the edge to Frazier, in a 15 rounder, by decision or a stoppage in the last 4 rounds. I wouldn't be completely surprised by Charles winning a close decision. Both fighters end up busted up.