Obviously, Canada and the United States together represent a big space, and both countries have limited resources when we're talking about such a large area. A key tenet of the NORAD agreement is that the commander of NORAD, who is an American four-star admiral or general, whose deputy is always a Canadian, normally a three-star air force general, has the authority to move air assets that are assigned to NORAD back and forth across the border, depending on the threat or the need to position aircraft for a potential threat.
One of the benefits of being in this NORAD agreement is that we're essentially pooling our resources given the difficulty of defending such a large continent. Those decisions are taken by NORAD and that's all covered under the NORAD agreement.