In the Canadian arctic-town of Churchill, Manitoba, the community works together to keep children protected from "the paws of the dozens of [polar] bears that migrate through here at this time of year."

Starting in August, polar bears begin migrating north from summer mating grounds to Hudson Bay, where the ice from which they hunt seals is beginning to form. For Churchill, situated on the bay's shore, that migration peaks around Halloween. The town and its surrounding area can see up to 20 bears a day.

Ms. Finlay's 4-year-old son Cameron was surprised to learn that the world's largest land predator isn't a part of every child's Halloween. "No bears?" he asked of trick-or-treating in Toronto.

Dressed as a mix of Ninja and medieval knight, Cameron said he isn't afraid of polar bears, which can be as long as 10 feet and weigh up to 1,400 pounds. Come Wednesday, he'll be prepared. "I'll just pop out my sword and start fighting," he said, unsheathing a plastic Samurai sword.