I s'pose you have carpenter ants in Canada--which are the "big, black ants" we have in the mid-Atlantic US.
They colonize wet, rotting wood, so they are commonly seen in areas where overflowing gutters, inadequate caulking and other water-leaking situations affect the surrounding wood.
I like to think of carpenter ants as an "early warning" system for carpentry, plumbing and like problems, rather than as a pest control problem. Get rid of the damaged wood and the source of the water that caused it, and the ants will go away. Baiting with poisons or worse, spraying, just treats the symptom (ants) rather than the root cause rotting wood).
Maryland Extension has a good fact sheet with more info:http://www.hgic.umd.edu/_media/documents/hg115_000.pdf