Learn French
as it's spoken on the street.

French sounds different depending on which side of the Atlantic, and which city, you land in. Paris and Montreal are close to 400 years and one ocean apart linguistically, even though they share a grammar.

Paris speaks the variety that forms the basis of standard written and broadcast French: precise liaison rules, clear stable vowels, and a level of formality (the tu/vous distinction matters and gets noticed) that textbooks generally get right. What textbooks miss is street level Paris, particularly among younger people and in diverse neighborhoods: verlan (backslang that flips syllables, so laisse tomber becomes laisse béton), North African Arabic loanwords, and a habit of dropping the ne in negation that turns je ne sais pas into je sais pas in almost every casual sentence.

Montreal is a different linguistic world. Québécois French diverged from France French roughly 400 years ago and kept developing on its own: the ti and di sounds affricate into tsi and dzi before certain vowels, the nasal vowels land differently, and English loanwords get folded into French grammar in ways Paris never developed (char for car, magasiner to shop, dépanneur for corner store). Add a set of religious term turned swear words (sacres) unique to Quebec, and a French-from-France speaker sometimes needs real adjustment time to track fast, casual Montreal conversation.

If you already speak one, do not assume the other comes free. The grammar transfers. The ear does not, at least not immediately. Start with the city you are actually moving to.