How do you say this in French (Canada)? seventy, eighty and ninety? soixante dix, quatre vingt, quatre vingt dix or septante, huitante/octante, nonante

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The most common use is soixante-dix, quatre-vingts et quatre-vingt-dix. I believe in Québec and France these are the only used. For Belgium and Swiss, I think they use septante and nonante, but I don't know if it is in general or specific to some regions, so don't quote me on that ;)

Note: If you are wondering why "vingt" takes an "s" in "quatre-vingts" and not in "quatre-vingt-dix" , it is because there is a silly rule concerning the plural of numbers. All are invariable except 20(vingt), 100(cent) 1 000 000(million) and 1 000 000 000(milliard).

20 and 100
If they are multiplied (4x20)(2x100, 3x100, 4x100, 5x100, 6x100, 7x100, 8x100, 9x100) AND they are not followed by anything, you have to put a "s".

eg.
300 = trois-cents
313 = trois-cent-treize

Million and milliard
Starting from 2, you have to put them in their plural form (s) if they are multiplied. Unlike 20 and 100, they don't have notable exceptions. :)

Note 2
Since the arrival of the new orthography, you simply put a " - " between all numbers.

There are many more rules (traditional and new ones) concerning numbers and I think I have strayed a bit from the question, but these are the most important ones and I thought they could help since you are learning 80 ^^ I hope it wasn't too confusing.