Since you don’t have national level extracurriculars or haven’t made a huge impact where you live, your odds of being among the handful of French kids admitted to Yale, Harvard, Princeton, MIT, etc. are almost nil. As you recognized yourself, you’re starting a bit late when it comes to EC’s, essays, etc.
That’s okay, there are LOTS of prestigious universities in the US - unfortunately they’re also very hard to get into 
but
I’d say your odds for an optimal combination of very strong math/econ programs and a non-zero shot at admissions would be:
- UMich LSA Econ/Math and either LSA Honors (highly selective, deadline may be past) or Residential College (quirky but interesting community and a good way to form solid bonds if not in Honors, look into it)
- Williams (“Little Ivy”, highly selective, except that unlike Harvard it is need aware meaning your being full pay will be a nudge in your favor + especially good for math + very, very strong network)
- Bowdoin (NESCAC, same idea as above)
- Northwestern, you can major in Economics and add a minor in Data Science, Statistics, or Business/Finance. Or you could stand out and apply for Economics/American studies, or Economics/History (because Economics is a much sought after major there and after all your HS background suggests American Studies or History wouldn’t be a stretch, and thus would be another little nudge for admissions.)
- NYU, definitely, CAS (Economics/Math) or Stern (Econometrics&Quantitative Economics). Although Stern is more selective, based on your interests and background, that - Econometrics- the major I’d pick.
- Northeastern (Honors), Data Science&Economics or Math&Econ; they have paid co-ops and professional experience/motivation is very strong there.
Combined Majors | Undergraduate Admissions
WRT professional experience: Typically you’d get internships or a co-op, then an OPT (you’d be able to work for 27 months, after which either you start an MBA, a Master’s, or your employer jumps through the hoops to get you an H1B visa, which is currently literally a lottery but may change down the line.)
If money truly is no concern, then you could apply ED2 to one of the above that offers it, and RD for the others.
Wrt Canada: McGill, UToronto, and UBC are all topnotch, yearly variations in rankings are meaningless in that regard.
Look into Waterloo for Math/Econ, too, especially if a paid co-op would be of interest (likely useful if you plan on going for an MBA down the line).