Here is what I've observed from the behavior of each country after spending years on 4chan's flag boards. Note that these are just commonalities that people from each respective country seems to express, this isn't a catch all. Also, any country which I do not elaborate upon has too small a sample size of posters to discern any characteristics in length. All pics are unrelated.
>Canada
The non-Quebecois are friendly, but they can also be somewhat gullible and they get butthurt easily. On the other hand, Quebecois come in two forms: either they get butthurt a lot easier than other Canadians or they have really good bantz.
>USA
There are too many Americans on 4chan to list any coherent stereotypes. The USA is a very large country and there are a lot of regional differences, so it is hard to create a cohesive stereotype for American posters. There is the stereotype that Americans are dumb, but there are plenty of smart Americans and midwits as well.
>Latin America in general
Friendly, laid-back, great taste in memes. Very shitposty but in an entertaining way.
>Mexico
See Latin America but better banter, honed over years of Trumpposting.
>Brazil
Similar to Latin America but they love making self-deprecating Brazillian jokes.
>Argentina
Mostly the same as Latin America but they have an obsession with race, the whole "Argentina is white" meme exists for that reason.
>Caribbean
Only Caribbean countries I have seen multiple posters from are the Bahamas and Trinidad. They're both friendly and laid-back with a lowkey sense of humor.
>Portugal
Pretty lowkey, they can go one of two ways: either great bantz or get butthurt easily. Reasonably friendly, but the saudade is real.