I was last there about 4 years ago, we caught several lake trout by trolling deep divers while paddling- usually they were on points and when the crankbait was digging bottom (i would guess 15-20 feet) we would catch some. The time was mid july. Not sure about earlier or later in the year. They are tasty and battle well, and I think spent much of the year in very deep water but we seemed to luck into them. Usually the crankbait was a deep fat rap, but I think it was the depth that was most important. Good luck.
ps- most of the ones we caught were in Quetico, but that is where we fished the most.