Canada is a hot market for fiberglass inground pools, so if they can handle the winter freeze/thaw cycles . . . I think WI and all other norther US climates are just fine.
Freezing Water, So What
The freezing water inside the fiberglass pool doesn’t affect it. Like any pool, you need to make sure your pipes are winterized and free of water, but that isn’t new information.
Location, Location, Location
Do Fiberglass Pools Work in WI?
Where you are located in the North America, is what is used to determine HOW you install the fiberglass pool . . . not if you can.
In the south you can use sand as it will not hold water as where in the North you want to use more rock. This is a discussion for another blog listing, it can get pretty heated among pool contractors, but for now know that you can put your pool in any North American Climate!