at the end of the Gunflint trail, there's a put-in on Saganaga Lake we use - we typically camp on Long Island on Saganaga, which is adjacent to Quetico and do day-paddles up into there. Power boats (25hp max) are allowed on Saganaga, but not in Quetico - a couple of things to heed, though.
1. BWCA requires permits, which you can apply for ahead of time and on-line, but have to pick up at a ranger station (most likely Grand Marais).
2. if you go into Quetico, you will need either a passport or the Canadian remote area access pass which you have to apply for early by mail, but I'm not sure what is required now - given the border entry changes etc. you would want to check. You will want to do this, as there is a Canadian ranger station RIGHT in the mouth of the entry bay on your way to view Silver Falls or some pictographs and the Canadian's expectation is that you will stop by and check in - with pass in hand.
3. July is prime bug season, so be prepared and the lake(s) can be heavily fished with a lot of competition for camp sites.
It's a nice 3 day trip.