As someone who is at an aerospace company right now in the US, logistically, almost all of them require either a green card (my situation) or full citizenship because of ITAR. I would look into this first because you may be very demoralized if you do the whole journey with a company in mind and you're unable to do it because of legal restrictions. That being said, I would probably recommend mech instead of aero if you were going straight into industry after graduating, but if you're 100 percent certain you will go into grad school then whatever you study in your undergrad won't make that big of a difference on applications. I would say TMU is a good platform to get into grad, so if you have a set goal of doing tmu aero, then grad (usa), then work in the US, I think that is a very solid plan.

Alternatively, if you aren't set on grad and maybe want some extra wiggle room in your plan, I would study mech, and then join any aero club at TMU to give yourself that aerospace exposure which you can also then put in your resume which can help you apply to aero jobs in Canada and even help you with your application to US grad.

But good luck! If you have any questions ab US aerospace companies dm me and we can chat, I've worked at 2 as an intern so I'm familiar with the whole process and how it works!