The crown had already assured/conceded them a measure of autonomy, particularly where it came to their Catholic religion. Look up the Quebec Act of 1774.

The Québec Act of 1774 gave quite a few things to French-Canadians living in what is now Québec, including the right to practice catholicism and keep the Civil Code. This made Québecois people (an anachronisistic term but using it for the sake of simplicity) quite happy with their situation as they were in a favorable situation.

Now, keep in mind that the Québec Act ended up pissing off the American Colonies and certainly added to the woes of the American people. Although not the cause of the American Revolution, it certainly added to an already tense situation. After all, the Colonies had been requesting a few things and yet, London was giving the favourable terms to French-Canadians. In all likelihood, there was more animosity between the two people than there were discussions to join forces.