While the government sponsors the jobbank is the official Canadian job bank site, my experience with 15+ years in HR has been that with some exceptions many of the large firms whether IBM, Purolator, KRAFT etc don't 'usually' use the government site. This doesn't mean you shouldn't use it and set up your alerts, but many of the large companies use job boards like www.workopolis.com. Mega-job search engines like indeed.ca and eluta.ca will also help you search multiple job bulletin board sites at once. Careego.com has an embedded link to indeed.ca in addition to giving valuable information about the realities of job searching in the Canadian marketplace.
You should really review many sites and determine which sites are giving you the best searches. If it's the jobbank site- then great, if not then use whatever site is providing you with the best opportunities.