Perhaps I can add to that.
If you look at where the VIN appears on the vehicle, it appears in a number of places and it appears for the purpose of actually identifying that part of the vehicle or the vehicle as a whole. The licence plate, which is issued under a provincial regulatory and legislative framework, is used for different purposes as opposed to identifying the different bits and pieces that go into making the vehicle.
So a literal interpretation of the definition of VIN would not include a licence plate, because a licence plate is not offered for the purpose that a VIN is.