Go online and reserve your park stay.
Reservations at Ontario Parks
You can see the Park, what it has to offer, your site, etc.
Some suggestions from experience -
Sandbar Provincial Park - Outside of Ignace (About 4 hours from Ontario - Manitoba border.) Great Beach, Great hikes, great sites!
Stop in Thunder Bay and see the sights too! Fort William Historical Park is something you should see at least once - it is amazing!
Thunder Bay, being arguably in the centre of Canada, has lots to do, see, places to eat, gear up, whatever.
Another great Provincial Park is Neys P.P. right on Lake Superior. Very historic - and old POW camp is there, the beach is amazing, the hiking and the views are so beautiful that members of the Group of Seven spent some time painting there. Look it up - Lawren Harris.
Keep Going along Lake Superior - Chutes P.P. is Great. White Sands is very nice and, as far as views and experience - Lake Superior Provincial Park is really, really nice.
If you have never been this way before, from the Manitoba - Ontario Border to Thunder Bay is about 7 hours, from Thunder Bay to Sault Ste. Marie is about 8 (towing), and Sault Ste. Marie to Toronto or Ottawa is about another 8.
Be prepared to stop, but you will really enjoy the journey!
Best of luck!