A grandfather clause carried over from the old British North America Act guarantees each province the same number of seats they originally received upon admittance into the Dominion and on that base every province gets new seats in keeping with population growth. (Although Quebec has not added new seats in a couple of decades - that number remains at 75.) The number of seats keeps growing with every federal census so unlike in the United States, no province can lose seats because the size of the House Of Commons isn't fixed at arbitrary number by law. As of the 2001 Census, there are 308 members in the HOC, though that number will go up again after 2011.
(Denny Crane: "I Don't Want To Socialize With A Pinko Liberal Democrat Commie.Say What You Like About Republicans. We Stick To Our Convictions. Even When We Know We're Dead Wrong.")