Assuming you can get across the border by then, you can’t really go wrong with any of the provincial parks along Lake Huron and Georgian bay. We have done them all many times. Beautiful beaches along the lakes and lots to do as they are all close to small scenic towns.
Craiglieth is a little small and right along the highway and Sauble Falls is split in half by a highway where 1 side is nicer to be on than the other but otherwise not a bad thing to say. It can be difficult to get a site though as they are all popular. The reservation system starts 5 months in advance of the day you want and you have to be quick at 7am to have any chance.
Feel free to pm me if you have any questions on any of the parks.
