If you're talking about st. george's or ross, both schools will give you the opportunity to become a very good physician. Whether it's a solid foreign or u.s. school, what you get out really depends on how hard and how dedicated you are to learning the material. USMLE is a an exam that is universal, there is no difference if you go to a caribbean school or u.s. school. Some foreign schools will prepare you better for the exam, but the exam itself is the same for everyone.
If you attend a foreign medical school you will need to score higher on the USMLE to be competitive, unless you really impress someone during clinical years and get an amazing reference. There are some PD's that are will not accept any foreign grads no matter what their scores are, research experience, amazing lor's, etc. Before you commit to one of these schools, make sure you do a lot of research and think about if its the right thing for you...if you're a borderline applicant, meaning that if you took some extra classes and improved your gpa or low mcat score, you might want to try to get into a u.s. school before you attend a foreign school.