Rob,Here is a link to a list of National and Regional Broadcasters in Canada: http://tv.zap2it.com/resources/stations/ca/
As far as a centralised location to find these positions, I haven't really seen anything too impressive. www.showbizjobscanada.com is one site dedicated to this but only has been up since March and there isn't much in there. I think your best bet is to apply directly to the tv stations or just surf the different job boards (monster.ca, jobs.com, etc) and see what you come up with.
Best of luck
Harry