Resort towns packed with families and expensive hotels are always dry without exception.
Incall isn't a possibility for obvious reasons. Outcall is the nearest large city willing to drive and charge you $$$$ to do so. Then you are faced with having a SP to your room looking out of place with everyone in ski gear and with kids running down the hall to the pool. Or your co-workers walking by your room at the time of the visit with the SP knocking on your door.
Best way is to make a pit stop for the hour in the large town/city you pass through, in this case Barrie. Or just take the 401/400 route there and pass through the very well serviced Toronto area.