Don't do it for the money, do it only if you want to be in the military, as a primary care physician. That goes especially for north of the border, since if you enroll in the motp, you are REQUIRED to do a residency in family medicine, and they only pay for three years of medschool, not four (but require 4 years of mandatory military service post residency - sounds like a raw deal to me). You can of course try to do another residency afterwards, but that seems like a colossal waste of time.
A better idea would actually be to go through medschool and residency with loans on your own, THEN join the military. That way, you practice in the field you want, and the military will give you a 200k signing bonus, which should take care of most of your loans anyway.