You would be lookng for DanC here on the board, he is the man when it comes to late summer Nipigon fishing.
I have only been there in the spring and that ws off a big lake boat charter fishing from the Shakespears west.
BIG water , please pay it the respect it deserves.
Try the mouth of small bays that have creeks coming in to them, on the rock transitions to deep water you should get some awesome pike fishing.
Not sure where the brookies spawn but they should all be coloured up then.
Wish I could tell you more.
Darren