A large percentage of programs unfortunately won't accept residents on H1B's as it demands extra paperwork (with specialized ancillary staff) and thousands of dollars. Of the programs that do sponsor H1B's, you will still be at a disadvantage relative to US MD graduates since your school is likely an unknown commodity to the admissions committee (unless your school is among the top few in your country). Additionally, there is an explicit expectation that schools should favor US MD applicants as the government subsidizes schools with taxpayer dollars.
Sorry for the gloomy assessment. Just wanted to be realistic. That said, hundreds (thousands?) of international grads match every year - some of them at the top programs in the country. So it's definitely not impossible; just an uphill battle.
