There's a lot of pretty important Canadian military projects that could use the extra infusion of cash. Mostly related to the Navy and Coast Guard. We could re-onshore ship-building in Halifax and Vancouver and expand coastal patrols. We need much better icebreakers.
9 billion could be committed quite fast in a pinch, IMO.
IMO, another worthy project would be preparing for an insurgency in the event of a US invasion. We could establish caches of weapons, food, etc all over the country for use by rebel forces. Boltholes in caves. Train Army personnel in insurgency tactics. Build up distributed drone manufacturing.