There are really two ways to take this issue. The first is to relegate the model to Canada whereas the second would be to apply it to other countries.
First, strategically, Canada does not have a pressing need for a large military to secure their borders. The ONLY adjacent country is the US of A and I dont think we will be attacking anytime soon. Not to mention the fact that Canada is our neighbor and a mounting security threat to her will also cause us concern. I doubt that Canada would have to fight alone.
Second, if you are referring to more civilan (Police, DEA, etc.) security as opposed to military security, then mandatory military service is not the way to go.
On the whole, it has both good and bad points. First, a dirtbag is a dirtbag is a dirtbag. No matter what training you pound into his brain or how many times you teach him discipline, he will be a dirtbag. He just might end up being a well trained dirtbag. Unfortunetly, you could be arming the very people you would have to fight later with the knowledge of your training and tactics.
Second, a mandatory anything makes people angry, especially if you start telling people to serve in the armed forces. You will get all kinds of people in there who absolutely hate every moment of it and will take that experience to heart on why the military or perhaps the Canadian government is evil (which its not). The would definetly put a damper on patriotism.
Finally and most importantly, not everyone should be in the military. As a member of the combat arms, it is very important to me who the men to my left and right are. If they are not willing to protect me with their lives, as I am for them, then I will die. I dont want average joe who hates the military and will not do a good job watching my 6 in a combat zone. I expect my peers to do their job 110% and I will do the same.
THat being said, I think some type of mandatory civil service could be good. Having the population choose where they work gives them a hand in it and allows people to have a peek into the different areas of government, be it the military, LEOs, park ranger, etc.
Qui tacet consentire.
Igitur qui desiderat pacem, praeparet bellum.
Nec Aspera Terrent.
Vir sapit qui pauca loquitur.