I grew up in Windsor, Ontario...about as far south as you can get in Canada. Even there, keeping a pond at 60+F would be a daunting task. There are, however, species of gar that occur naturally there. Spotted Gar are found only in the southernmost tip of the province; they were listed as Threatened for years, and I believe have now been upgraded to Endangered. You'd need to check with the MNR but I'll bet they are completely protected and illegal to catch or possess.
But Longnose Gar are common all throughout the southern third of the province, and are pretty easy to find and catch. They may not be as massive as an Alligator Gar but they can be up to around 5 feet long. They have a very exaggerated, very elongated and slender build, actually a lot more exotic looking than Alligators. I kept them several times many years ago, they do very well in aquariums and are obviously suited to the climate.
I've always wondered how they get by under the ice during winter, with no access to atmospheric air for breathing. I assume they are just so inactive and semi-dormant in the cold water that they don't need much oxygen.
In Windsor, a pond of 2 or 3 feet in depth would be fine. The further north you go, the thicker the ice and the deeper the pond will need to be. In Manitoba where I live now (about an hour north of Winterpeg) four feet of ice is common. Ponds are either seasonal or very deep or very, very challenging.
Yes...it's really, really cold...