I did some research into this to solve the riddle. Canada is not a big producer of the metal, so there's no economic incentive. They don't process a lot of eWaste, although India does and they are against the ban as well. Aha, how about this. According to the EPA:
The primary sources of mercury to the environment are fossil fuel burning (primarily coal) and solid waste incineration (Nriagu & Pacyna, 1988). Power plants in the U.S., according to U.S. Environmental Protection Agency, are one of the main sources of mercury pollution—48 tons a year.
Good thing the EPA took our power plants off the regulated list for Mercury in March 2005. Maybe Canada plans on burning up a lot of those Athabascan Tar Sands they are developing, generating a lot of mercury vapor in the process, and they don't want to be hypocrites? Sounds plausible to me, could be that's mystery solved.