As a couple of others have mentioned, make sure you get the opportunity to do research (included through study abroad) and would like to have a few different fields. Getting into top grad schools will depend more on your research, PGRE and GPA. My son is soon to graduate in physics from a large state school, very good gpa and pgre scores, and has had the opportunity to do research around the world and has been published a few times. His advisors are steering him to only top schools in his field.
Here are two theoretical physicists who are active at Lehigh University. I would write to them, and ask about undergraduate research upfront:
theoretical particle physicist:
https://www.lehigh.edu/~sec415/
theoretical biophysicist, they use condensed matter theory and apply it to the human body!
http://athena.physics.lehigh.edu
Professor Kim at Lehigh U studies experimental and theoretical plasma physics:
https://www.lehigh.edu/~ywk0/ywk0.html
RIT is very strong in experimental materials physics, experimental astrophysics and experimental optics,
if any of those interest you. I think math is better at Lehigh, though, so for theory I would still choose Lehigh,
if you are limited to those two for best international student financial aid.
Because you are an international student, you will not qualify for any NSF funded summer REU that requires citizenship. This makes it very important for you to check if you can work on campus.
I do agree that Lehigh is very small in physics, for undergrads, but still with two active theorists, may work out for you to get a super education IF either of the two active Lehigh faculty will mentor and tutor you and allow you to work with their PhD students and work with you directly. ASK THEM NOW via email. If those Lehigh faculty do not respond, that is a bad sign for Lehigh and studying theoretical physics there. Although RIT is really not focused on theoretical physics at all, so I still do not recommend it, unless you want to study experimental optics, astrophysics or materials physics.
. Case Western Reserve has strong math and physics, and a few theorists that take undergrads, see Michael Hinczewski at CWRU, not sure how many international students get aid there. I would go for the larger state programs in physics, if they have aid for international students. Thats doubtful unfortunately.