Yes, the exchange rate makes it a nice time to visit Ontario, and most of your trip will be in Ontario if you drop back down in Minnesota.
There are lots of Provincial Parks along your route in Ontario, most do not have drinking water at the site, so remember to fill up at the Park's central water faucet before set up. Some more remote Northern Parks don't have electricity either.
Oh, and watch your gas gauge in the North if you have a small tank.
As mentioned, and no different than in the States, the summer weekends, especially the long weekends, can be very difficult to get in; so consider reserving or arriving early.
Algonquin is nice, but busy. Killarney, Killbear, Lake Superior and Quetico P.P.s are also nice. There are many others. Bring your canoe or kayaks if you can. There is one National Park that we really like: Pukaskwa on Lake Superior, but most of their sites are smaller.
If you DO want to visit Toronto there are a couple of Toronto Region Conservation Area campgrounds close by, and you can avoid most of the traffic by going around on the 407 toll way (you might get a big bill in the mail though ...). But we just plan our trips there/back when the traffic is light and avoid the tolls.
And remember to have all the proper I.D. when crossing the borders.