Well, at the moment it is, in the rather unusual way that CSE is bolted onto the side of DND.
But I think there is a qualitative difference between physical defence of the interests in the land of Canada and the cyberworld, which does not look like that at all. There are places that are sort of in the middle ground. For example, biological terrorism has the same property, but it doesn't matter how good CBSA is, they're not going to be able to keep out anthrax that flows across the border from the south, for example. So we do need to move to a mindset that includes understanding that the defence of Canada is not entirely physically done.