If you apply out of HS, you're not applying MOTP - you can only apply MOTP once you have been accepted into a medical school (it actually used to be after you have completed the first year of a 4-yr med school, not sure if that changed).
Not only that, but if you're accepted MOTP, you can only do your residency in Family Medicine. Provided you remain interested in medicine, you might find your interest drifting to other fields. Maybe you'd rather be a vascular surgeon, or a pediatrician, or whatever - if you're in MOTP you don't get the choice.
For structuring your undergrad (the MD is also considered undergrad, which is confusing, but in Canada you need a minimum of 3 years' of undergrad before applying to med school, and generally a full 4-year degree if preferred), most pre-med programs pre-structure it for you, but check out the prerequisite courses required to apply to the various med schools. UWO used to have a bunch of very specific ones, but now appears to have dropped this requirement. Provided you include the prerequisites, you can pick any major you like for undergrad, you don't need to stick with whatever the school offers as a "pre-med" option.
As for A/N/AF - medical is a "purple" trade. Regardless of the environmental uniform you wear, you can be posted to an Army, Navy, or AF base. Whether you yourself are Army and the posting is AF won't matter.
