Since you are coming from Niagara Falls, you will be taking the Queen Elizabeth Hwy. towards Toronto. You might want to consider staying at Bronte Provincial Park which is about 30 miles West of Toronto and right off the Q.E. Highway (1.5 miles).
From there you could drive to the GO commuter train which takes you into downtown Toronto and public transit throughout the city.
As above poster recommended Killbear and Killarney Provincial Parks. Note that
Killarney is about a 45 minute drive off the main highway - the road is good though. You would want to be sure to have reservations at either of these parks.
Another provincial park l/2 mile off the highway heading north is Grundy. It is also quite nice but if you like hiking, then Killarney is much better. Killbear is good for sailboats and windsurfing, Grundy for canoeing.
You will not have problems finding facilities on your way to Sault Ste. Marie. It is a major highway that passes lots of small towns and some nice scenery.
PM me with questions and I can help with other suggestions. I live in the area.
2014 Triple E Regency GT24MB (Murphy Bed) with all the good stuff
towing a 2016 Jeep Cherokee TrailHawk
Berkley, the amazing camping cat missed dearly (1996-2012)