The population at the time was mostly based in the region of Quebec. They were not originally under the Crown rule but were of French descent.

After the French and Indian war, the colonies changed hands from the French to the English. They were culturally distinct. The French settlers were mainly Catholic as opposed to the American Protestants. They were given the Quebec Act, which helped placate many of their concerns regarding religion, at the same time the Intolerable Acts were passed, punishing Patriots for the Boston Tea Party. They had no reason to rebel and were geographically separated from the colonies via large swaths of wilderness.

This is also in the FAQ if you want more information.