From the first moment I seen James in the bathroom, I couldn't help but assume it was meant to be Sean Bean.
As for the others, there's plenty of characteristic fat guys who can play Eddy. They don't need to look like the game characters to pull the character off; they simply need to be able to play the character. So for Eddy, I'd pick this guy from Cabin Fever.
Mary/Maria, you'd need an actress that could pull off both roles (homely and sexy) and I can't think of any. Marilyn Monroe probably could, though. (Diaz is a terrible choice, she's as far detatched from the character(s) as possible!)