Well there is Quebec French and Quebec French. For that matter there is wide divergence among French dialects in France. As far as I can tell, there is a substantial difference between France and Quebec, but they are mainly intelligible. I don’t know much about Cajun, but Cajun is derived from Acadian (“Cajun” is a corruption of “Acadian”) which is New Brunswick and Nova Scotia. The one fact I can affirm is that a French Canadian friend of mine (from near Trois Rivieres) was a graduate student at Dalhousie (in Halifax) and met a French speaking student from Northeastern Nova Scotia and they could not understand each other’s French… They spoke English.