Looking for nature Princeton to Quebec to Chicago

Sepaq is Quebec province's well-oiled publicity agency for its extensive national parks.
http://www.sepaq.com/pq/index.dot?language_id=1
(PS: "National" means Quebec to Quebecois, not federal government. Bienvenue a Canada.)

You don't mention Ottawa in your itinerary, but if you do visit, Gatineau Park (not strictly a national park) is just across the river in Quebec, and has several hiking trails, more info here: http://www.ncc-ccn.gc.ca/places-to-visit/gatineau-park

Algonquin Provincial Park is probably southern Ontario's most famous wilderness/recreation experience. Think forest, small lakes, moose ponds, and the like. It's more or less directly west of Montreal by way of Ottawa. Further west there's also Georgian Bay on the east side of Lake Huron. The east shore has some great sea kayaking; Tobermory Peninsula on the west shore has more accessible family camping and some very scenic hikes along the peninsula.

More directly on your route, in between Montreal and Toronto, what about Charleston Lake Provincial Park, Frontenac Provincial Park or a piece of the Rideau Trail (a long-distance path between Ottawa and Kingston)? Hikes short and long, lovely canoeing. Frontenac campsites are walk-in or canoe-in only, which should get you nicely away from the crowds. Charleston Lake has those too, but also regular campsites and even yurts, though those may be fully booked at this point.

Yes, actually Frontenac has ONLY interior, walk-in and/or canoe-in sites. I have a real fondness for the place (it's where I started camping as a teen, without adult supervision, a few decades ago; I even blazed part of the Arab Lake trail a few decades back!) and still like to get out there for a day when I'm in the Kingston area. However, IMO Frontenac is best in spring and fall (and maybe winter?); mid-summer it's simply too hot and buggy, and lacks the kind of wildlife spotting opportunities and sense of big nature "wildness" of a place like Algonquin Park or around Killarney on Georgian Bay. The small lakes and ponds and second-growth forests of Frontenac make a nice break from the city, and it's a great, safe place to be introduced to camping, hiking, and canoeing, but it just doesn't make a big impression... (sorry, Frontenac - you know I'll always love you!).

YMMV

This is great information…thank you. I feel like we might need to visit 2 parks and spend more time…one in Quebec (that Sepac site is insane…wish we had a national parks site like that) and one in Ontario. I would love to visit Georgian Bay, but I think that is another trip. Algonquin might be too out of our way also since by the time we get to Ontario we will be in a rush. Frontenac does appear to be a good stop…but I hate bugs. Would Prince Edward make a good stop? Even if we don't have much time we like to stay in smaller places rather than the big cities, to try and get city living out of our bones before we return to the noise and grime of Chicago...

If all your looking for is a daytrip, a break from the city, rather than a camping experience, then Frontenac might not be such a bad choice in midsummer. The area right around the Visitor Centre is less buggy (though the trails can be a different story, as they go through wetlands) and makes a nice picnic spot - though when I was there last July, the rangers were demonstrating how to fire bear bangers to a group of visitors. Alternately, you could rent a canoe and get out on the water . Frontenac Outfitters is close to the park entrance, and you can easily ferry a canoe on a cartop carrier to the boat launch at Big Salmon Lake. Again, it isn't exactly Canada raw and wild, but Frontenac is a nice place - I visit every summer!

If you hate mosquitos, ummmm. Can you postpone the trip till mid-August or so? Fewer mosquitos then. Either Charleston Lake or Frontenac would give you a modest, miniature taste of the Canadian shield experience. Prince Edward County is more farmland and a few woodlots, plus of course the fine dunes and beaches of Sandbanks, and the views over Lake Ontario. It would be a pleasant place to spend the night after a day in one of the other two parks. The town of Picton, at least two years ago, still felt like it was in a time warp: the main street was like the Ontario towns of my all-too-distant childhood, right down to the angle parking and theatre marquee. Wellington and Bloomfield are pretty, slow, small towns too.

If hiking is your goal, then I think you actually have better options in the US: Vermont, New Hampshire, the Adirondacks - depending on your route, exactly. Most of southern Quebec and Ontario is highly urbanized and agricultural. The hiking in Frontenac is okay; it really works best if you consider doing a canoe trip. There are a series of mountain-parks south of Montreal (Orford, Bromont, Mont-Ste-Hilaire) that have some good hiking but they are nothing like the high peaks of the Adirondacks. The area to the southeast of Montreal - the Eastern Townships - is scenic and a pastoral way, much like Prince Edward County in Ontario. Both areas are gorgeous and great for touring but not to experience "nature." There will be more rigorous outdoors opportunities near Quebec City (but a bit past so not quite on your route).