Although Quebec French constitutes a coherent and standard system, it has no objective norm since the very organization mandated to establish it, the Office québécois de la langue française, believes that objectively standardizing Quebec French would lead to reduced interintelligibility with other French communities around the world, linguistically isolating Quebecers and possibly causing the extinction of the French language in the Americas.
Mutual intelligibility with other varieties of French:
Mutual intelligibility of Quebec French with Metropolitan French is a matter of heated debates among linguists. If a comparison can be made, the differences between both dialects are probably larger than those between standard American and standard British English, but far less than those differences between Brazilian Portuguese and that of Portugal or between standard German and Swiss German. Francophone Canadians abroad have to modify their accent somewhat in order to be easily understood, but very few Francophone Canadians are unable to communicate readily with European Francophones. European pronunciation is not really difficult for Canadians to understand; only differences in vocabulary present any problems. Nevertheless, Quebec French accent is mostly closer to that of Poitoi or of Normandy and also some parts of Wallonia.
In general, European French speakers have no problems understanding Quebec newscasts or other moderately formal Québécois speech. However, they may have some difficulty understanding informal speech, such as the dialogue in a sitcom. This is due more to idioms, slang, vocabulary and use of exclusive cultural references than to accent or pronunciation. However, when speaking to a European French speaker, a French speaker from Quebec is capable of shifting to a slightly more formal, "international" type of speech.
Quebec's culture has only recently gained exposure in Europe, especially since the Quiet Revolution (Révolution tranquille), and the difference in dialects and culture is large enough that Quebec French speakers overwhelmingly prefer their own "home grown" television dramas or sitcoms to shows from Europe. The number of such TV shows from France shown on Quebec television is about the same as the number of British TV shows on American television: they are seldom broadcast except on obscure cable channels.
And thanks to my friend Steve Faguy, because I stole the photo from his cool blog, which happens to be based on and in Montreal, speaking of Quebec.