“Their Operations Research major sounds so cool.”
I got my master’s degree in Operations Research (after getting a bachelor’s in math). I loved it, and have done well since with the degree. At least IMHO, OR is indeed a cool subject to major in, and fun, and useful for getting a job. I suppose anyone who calls a branch of math “cool” is not normal, but I am okay with that.
You should include an application to UIUC. I just checked and it is top 30 for both mathematics and economics. Being in-state it would be a bargain.
If you want to consider later getting a master’s in OR, at least in my experience having some basic computer science ability was very useful. Of course the same is probably true for multiple other subjects and majors.
I just noticed “Language study program in France”. This makes me wonder about whether McGill would be a fit.