The characters in The Count of Monte Cristo don't spend too much time worrying about the "free will" part of the equation. Usually they only stop to consider the repercussions of their decisions way after the fact. When things start going badly for certain characters, they feel that unknown forces have turned against them. Does that mean things really are fated to happen? The Count certainly seems to think that he's been tasked with carrying out God's will, but even he reconsiders his actions.
In the end, Dumas shows fate to be a convenient excuse for human failings, and justifications for the unjustifiable.