You could try White Lake Provincial Park. Great camping sites and beach for the kids, and the pike and walleye fishing is supposed to be great (according to the locals). You would need to trailer your boat up, but 12 hours and all highway. Many other great walleye, speck and laker lakes in the White River area.
Kwinkwaga lake is also close to White lake and is a smaller sized option with lakers, pike and walleye, and is a "roughing it" option in the area. Beautiful lake, although the dirt road in is not well maintained.