Here is a list of admission and FA policies of all US medical schools w/r/t international students. NAAHP: Medical School Admission Policies Towards Non-U.S. Citizens
Every US medical school requires that all international applicants complete their science and math requirements at an accredited US or Canadian university with a minimum of 2 years of in-residence attendance.
Even if do get a green card, admission to US medical schools has become increasingly competitive. Every year over 100,000 individuals take the MCAT exam. There are fewer than 19,000 available seats. There are no guarantees you'll be admitted to med school even with a green card.
There is very little FA for domestic US medical students. Most finance their education by taking out ginormous loans. (Average indebetedness at graduation $180,000+ for public med schools; $225,000+ at private schools.)
If you want to practice medicine in the US, the most cost-effect way is usually to complete your medical education in your home country, then take the USMLE exams and enter the US residency match program to complete your medical training in the US.
The Educational Commission for Foreign Medical Graduate oversees the certification of FMGs and their RMP applications. ECFMG | Educational Commission for Foreign Medical Graduates