Probably because Canada is such a sparsely populated nation that is 'out of the way.'
No one really cares to march an army up to Canada. If there is ever a tree or cow shortage, however, Canada will need to more jealously guard its resources... but, seriously....
It's a relatively low-pressure country where the population, simply due to how sparsely it is arranged, doesn't experience much social, governmental, or international pressure/stress.