I fished Gowganda the last couple of years, though I stayed at another resort. Back lakes are indeed better than the main lake, especially for walleye, but for smallies and pike, the main lake isn't that bad. I was there this June, and between my fishing buddy and me, we caught around 40 to 50 smallies a day on the main lake. No luck with walleye though.
The back lake above the fall, called Hangingstone, is a bass heaven. Literally every cast produces a hit; in fact, there are so many smallies that after a while, you might actually get bored (impossible, I thought, but it can happen, lol). The size tends to be smallish in Hangingston though, and at least for us, all the lunkers came from the main lake. As for walleye, Stumpy is superb. Trolling was a bit slow when we tried it this year, but it produced the biggest walleye, and once the sun began to set, we had non-stop action jigging by the small fall/stream. Getting to these back lakes is a pita, but well worth the trouble/cost.
If you decide to give Stumpy a try, take with you some HJs and orginal floating Rapalas for trolling. There are sunk logs everywhere in the lake, so 3 or 4 feet is the maximum depth that you can troll without getting snagged constantly. Deep diving lures are useless in that lake. Perch pattern worked the best for me.