Highways in northern Ontario are almost entirely two-lane with the odd passing lane here and there. The speed limit is 90 kph -basically 55 mph.
An oft-repeated joke in that country is that there are two seasons; winter and road construction. Plan on being delayed at some point(s).
Things are definitely more expensive up here and the two currencies have been pretty close to parity for some time now. Be sure to keep that in mind when budgeting for the trip.
Two highways cross northern Ontario:
Highway 11 which runs from North Bay to Nipigon (an hour or so east of Thunder bay) and has the virtue of being relatively flat and easy to drive.
Highway 17 -which is part of the Trans-Canada Highway- follows the north shore of Lake Superior and the scenery is nothing short of spectacular. There are some pretty steep grades though.
In either case, when you see a gas station it's a good policy to stop and top up your tank. They are few and far between in spots.
There is lots of wildlife all through there; lots of moose, lots of bears, it's a good idea to stay off the roads after dark if you can help it.
As mentioned, leave your gun at home. If you're worried about bears you can buy a can of bear spray at any Canadian Tire store.
You should have a good trip. It's pretty country and the people are generally nice. I'm more partial to the provincial parks but you'll have plenty of options. I used to spend a lot of time at Lake Superior Provincial Park just north of the Soo.
Othar than that, all I can do is advise against trying to exit the country at Thunder Bay. Unless your rig is extremely seaworthy