Maybe Opuntia humifusa (Prickly pear) cactus might be the best choice. They are native to Southern Ontario and may do well in your zone. I don't think they like wet soil so you will have to amend the soil with lots of sand and erect a shelter over them for winter. Hope this helps and I will let the experts suggest other cacti.

www.rom.on.ca/ontario/risk.php?doc_type=fact&lang=&id=20 8)

Cheers, Ryan

Thanks for the help. I might get some of those type for my little cabin on the south wall.
I will do my best for the wet protection.

I wish they were native here.
Maybe we are to close to the lake.

I have Humifusa from the coastlline. Its very tolerant of moisture, but can not take constant moisture - needs good drainage. The coastal plants have been flooded under salt water.

The only bad thing about this cactus is the fact that it turns on its side and becomes discolored during cold weather.

Yuccaman,

Check out http://www.rockgardenplants.com

I have bought lots of cacti from there and they all made it through winter. Also try Opuntia polyacantha. They have big pads and very cold hardy. O. Basilaris is also good choice. All mine made it with no damage at all. 😀

Regards,
Jay