One very important difference is the adoption of French Canadian words into the English vocabulary, eg: DÉPANNEUR (pronounced Day-pan-er) is ONLY used in Québec - not in any other French speaking country - to mean a convenience store; one of those open-all-night "mom 'n pop" stores. All English speaking people in Québec use this term. It is not used, nor understood, anywhere else in Canada. A second example is the word AUTOROUTE (pronounce OH-toe-route) to mean a highway (many-laned, high-speed road). It is pretty self evident when you look at the word - a road (route) for automobiles but is not used elsewhere.

CHECK is an example of a word that should be used the same everywhere but isn't. When I am at a restaurant in Quebec and I want to pay for my food I ask for the bill (la facture) not for the check like the rest of Cda (or the USA as I found out this week-end). A check is what you pay your bills with and in Québec is spelled the French way 'cheque' in both English and French.

I usually find out I've used a 'Québecism' when I say something and I get a blank look from the person I am speaking with.