There are some cacti native to Canada, most in the western half of the country (excluding the damp west coast) where the winters are generally drier. However there is also a species of prickly pear (Opuntia humifusa) native to extreme southern Ontario. With the right conditions (good drainage, full sun exposure), opuntia can theoretically survive on the east coast of the country, where I’m located.
Though I prepared an area last spring for some opuntia cuttings in my yard, I’m a little leery of leaving them out in the full brunt of the wet and cold fall/winter/early spring season cycle this year. Especially at their relatively small size.
With “an overabundance of caution” (a common phrase these days), I dug them up a few days ago and transferred them to a couple of pots full of gravel/perlite and some cactus soil. They’ll be stored in a partially shaded unheated greenhouse till April or so and should be fine. The increasingly cold temps will make them go dormant and lose most of their moisture content over the next couple of months. This drying enables them to hold on till the next warm growing season, when they begin to be able to absorb moisture again.
The Green Windowsill 