Basically, the federal regulator is the first filter, deciding whether the product is acceptable or not in Canada based on federal regulations, national security, etc. If it's not, end of story. If it is, then each province (constitutionally responsible for health care) applies a second filter to make sure the product is compatible with its own laws and local specifics. In practice, this is mere fine tuning as provinces seldom forbid something that's been approved at the federal level.
It's just strange that it requires approval twice, rather than being assumed to be approved unless banned.
But then I suppose looking at any government system with fresh eyes, they all have some quirks.