I'll second (or third, or whatever) the plug for Thunder Bay, since I live here. Following are the things to see in the Thunder Bay area:
-Kakabeka Falls (provincial park 30 km west of Thunder Bay; it's right on the Highway and you quite literally can't miss it)
-Fort William Historical Park (accurate rendition of this major 1815 fur trading centre, with period re-enactors and some period weaponry...but the focus is on the fur trade)
-Thunder Bay Military Museum (in the local armoury, at 317 Park Avenue, downtown north side; it's a small museum, but quite good, and includes a large display of water colours and drawings done by a German PW held during WW2 in several camps on the north shore of Lake Superior)
-Marina Park and the Sleeping Giant (downtown north side; a photo op sort of thing)
-Ouimet Canyon (about 40 km east of Thunder Bay; a spectacular, deep gorge with good viewing; the bottom contains a unique eco-system, called an "arctic disjunct", because the plants down there are normally only found in the arctic. However, low light levels year-round at the bottom make it a cold, dry, dark place)
-Eagle Canyon (very close to Ouimet; walk across a 600' long suspension bridge over a 150' deep canyon...this is Canada's longest foot suspension bridge, but this one, unlike the others above, will cost you some money)
I'd also recommend taking Highway 17 west of Thunder Bay, along the north shore of Lake Superior, if the weather is nice, and making your way to Sault Ste. Marie. The views along the lake, especially at Rossport, Terrace Bay, Marathon and south of Wawa, in Lake Superior Provincial Park, are spectacular. I particularly suggest a stop at Old Woman Bay, just south of Wawa. There's a beach, if you don't mind swimming in Superior (the water rarely breaks 5 or 6 degrees C, even in the summer) and some amazing cliffs. Also, Rossport is a true hidden gem; there's a bunch of little craft shops, a restaurant and some great scenery, just by leaving the highway for a half hour or so.
If you take Highway 11, it's faster to North Bay (where 17 and 11 cross again), but the scenery is much less interesting once you get away from Lake Nipigon, until you're back in the Temagami area--about 600 km worth of moose pasture and jackpine flats.