Maybe ypu caold give it to a friend, if you’re absolutely against the frog being in your house. If temps are good (heat lamp etc.) attic or garage might work. Idk much about winter in Canada (being from Houston, lol what is winter) but you said freezing so he prob wouldn’t survive if you let him go without shelter. Although he is native, so he may be adapted. Since northern and southern leopard frogs are different, I don’t know much about the northern variety. So, basement or attic would be my suggestion. If not, do you have those water meter boxes in the ground? They are well insulated and I find frogs and toads there all the time, even in winter.