Not only loans, but generally Canadian applicants who are applying to the States have the money or the means necessary for getting an MD in the States. If I were to matriculate in the States, my tuition would be paid for by loans, parents, and my older brother who is already working and would provide the lion's share of the money needed for tuition. If I were to get into McGill for 2011, my tuition would be $5k/year, which is even less than my undergrad tuition. Compare that to a school in the States where I'd be paying 10x that figure or more.
I remember my parents having to sell off their two cars just so my brother could graduate from dentistry. A few years later he bought my dad a brand new BMW 335i and my mom a brand new Civic. There has been a lot of investment in my family.
I know many friends at my university who are not even thinking about applying to the States or internationally because they simply cannot pay for it even through loans, which is a depressing thing to hear.