Neither is exactly a "bum". Chisora is a decent domestic-level fighter, and Fury is a limited big man who can use his size to reach about the same level as Chisora. Both are fortunate to be in a country where even mediocre fighters get ample media attention. If these two guys were in the USA, they would go through their entire careers without ever being mentioned by mainstream media.
I'd love to know the odds on this fight. I bet Fury's size and mouth make him the favorite, but he can't win this one. There's money to be made here.
You can get good odds on Tyson belive it or not. I've had a nice double with Kevin Mitchel last week, so fingers crossed. He's around 11/10 - Chisora 4/6