Really? I think this may come as somewhat of a surprise to both Canada and the US. I'm struggling to see where Canada and the US share any defence strategy outside of regional air defence cooperation (NORAD) and NATO.(...) Canada will follow what the US does as they have in effect, a joint defence strategy.(...)
Leaving aside the cold war, Canada's interest in NATO was that Europe (especially the UK and France) provide a counter-balance to the US, dilute their influence in defence matters, and helped discourage them from acting unilaterally (with US unilateral action being viewed as potentially destabilising and erratic).
Canadian foreign policy is centred around tying the larger powers into multilateral institutions and discouraging unilateral actions. This is the strategy of a lesser power attempting to keep from being crushed between the major powers. US policy towards Canada is that occasionally they remember that we exist.
This is a political and diplomatic benefit, not something on the defence level. The average Canadian sees little if any direct defensive benefits today from NATO. Rather, making useful contributions to the defence of others is viewed as being the price of having a seat at the table when decisions are made which may indirectly affect us.
Hence, Canada has a vested interest in seeing that NATO remains viable and that the core nations of NATO (the ones capable of wielding influence) remain members.