Canada has a population of about 41.5M people. Fielding a military of a few hundred thousand reservists should be entirely doable.
For comparison, Finland has a population of about 5.5 million, the active military is about 24k, primary reserve is 280k and secondary reserve is almost 900k soldiers. These are people trained 6 months or more.
How useful would a person trained for 1 week be in a pinch? Not as useful as one with 6 months training, but infinitely better than one with no training.
Ukraine is drafting personnel who have no prior training for 1.5 months. Finland trains the reserves continuously and would massively increase training in the event of a crisis developing.
Knowing who will go into what organization to do which job and basic familiarity with gear will help massively.
Marcus truly seems like a wise man. Shame he is dead.