(Gravenhurst, Ontario) About an inch in length, very long fur, had suction-cup like feet and a prominent orange ridge of fur on its back.
Your caterpillar is a Milkweed tussock moth caterpillar.
This caterpillar feeds on milkweed as the name suggests. The eggs are laid close together and the larvae when they hatch feed next to each other until they get to the last couple of stages. They can defoliate any plant in the milkweed family.
This insect is found in the eastern half of North America.