You mention Longbow. My preference is Anicinabe Park in Kenora,
www.anicinabepark.ca/
We have stayed there for up to 6 weeks during the summer for a dozen years or so and have met countless folks like yourselves that are traveling cross country. Some of those have stayed an extra day or two, or planned to stop for longer on the return trip. Near the WalMart, Canadian Tire, Tim's etc. Plan to take in the MS Kenora dinner cruise to see some of the lake while your there. 64,000 miles of shoreline, more than Lake Superior. A destination for thousands of people every year. Large sites accommodate the largest RV's.