Ontario is fairly well protected by fast moving rivers and great lakes. It will take a while for zombies to make the crossing. Still a fair head start for us Canadians. New Brunswick and Nova Scotia have no geographic barriers, but northern Quebec is protected by the wide St. Lawrence river. In the south it is narrower, but it is still better than nothing. Manitoba, Saskatchewan, Alberta, and British Columbia are far from major American cities. All in all, I'd say that there is still a long enough head start for us to evacuate to the north, provided the zombies originated in America and there is plenty of media coverage. Especially if the apocalypse takes place during the winter.