Don't know if you still need this information (I've been out of touch for a while) but...
1. Does Canada have an equivalent of a Department of Homeland Security?
I think the agency you're looking for might be CSIS. Check out this site:
CSIS 2. What agency (air force?) monitors Canadian airspace?
Well, I'm pretty sure we employ an Eskimo in Tuktoyaktuk with a pair of binoculars to watch the sky for invading aircraft. Although... come to think of it, do we provide the binoculars or does he?
(Just kidding, of course)
ML