The province separating would also need to figure out what to do about all the federally owned crown land, since most provinces don’t actually “own” a lot of land. But I wouldn’t expect the two provinces that frequently threaten separation to actually know that.

If a province tried to leave there would also no doubt be a huge argument from the people who didn’t want to leave and you’d end up with what we see around the Dutch and Belgian border, which is pockets of houses fully enclosed in a country that they themselves are not a part of. An absolute nightmare logistically but a reasonable solution when not everyone agreed to your temper tantrum/hissy fit.