I'm from Michigan and I spend 4 to 6 weeks a year fishing in northern Minnesota mostly in the BWCA.
I have been to Rainy lake a few times, the lakes hold all species, but if it's Walleyes you're after I have had my best luck at shorty's reef and nearby Erickson's reef they're in Voyageur National park, and they're both just south of Harrison's Island. we used leeches and minnow's on a lindy rig. Red lake has a good reputation but I have never been there.
hope this helps