I been going to Quetico for 22 years, since I was 13. I missed last year because our baby was born in April. I'll be going this year for 11 days in early July. I been all over. This year were heading out of Lac La Croix. Plan on fishing the area of Suzanette, Comnee, Burt and Brent. I like to make sure my trip goes thru good Walleye and Lake trout Areas. SM Bass and Pike seem to be everywhere. You right, always great fishing no matter when you go.
Quetico seems to be getting more people in the last 5-6 years but we still only see a few groups after a couple days of travel. I've caught some 30" walleyes from a few of the above lakes and my biggest Laker was 42". After my trip, its hard to get into fishing locally.
BTW, Canada has a work strike going on, if it isn't settled the park won't be open at all.