I am struggling to understand this sentence. If you want a good understanding of mathematics, why not study…math? Or, do you mean that you are interested in the quantitative aspects of economics?
Well, nobody has to apply to any US college! By “top” do you mean “internationally famous name”, aka Harvard / Yale / Princeton / Stanford / UChicago? The acceptance rates for international students are a small fraction of the acceptance rates for domestic students at all US universities. At the most selective level, where overall acceptance rates are under 10%, you are looking at seriously small odds. Harvard currently has 7 undergrads (total) from France, so perhaps 1-2 students/year? Are you that level of outstanding relative to the other French students who will be applying?
When you ask about the reputation of Canadian and UK unis in the US: the answer depends who you are asking and why. Ask the typical person on the street, and they probably won’t have heard of the most of the unis you list. On the other hand, grad schools admissions teams will know all of them. The top MBA programs in the US will expect a minimum of 2 years work experience; based on the current crop of Harvard MBA students, it looks like 3-5 years is typical. The name of your undergraduate university is not irrelevant (and the range of names that are seen as strong is broader than you might think) but what you do in the intervening years is highly relevant.
For an MBA? Nearly impossible to say- and really not a relevant question for you. It’s impossible to know how many even want to go, much less how many apply. Even if the data was available, it would be difficult to extrapolate the meaning for you, not just because the sample sizes would be small, but because of the work interval between college and grad school introduces an enormous variable that is impossible to quantify.