I've fished Gaspe in the Fall for the past couple of years. Unlike New Brunswick, guides are not required in Quebec.
That said, I think that for at least the first visit or two, a guide can be very helpful and useful for learning the rivers and how to fish them. If you are looking at the rivers on the tip (York, Dartmouth, St. Jean), I'd definitely recommend contacting Ann Smith who runs Quebec Sporting.
If you want to fish around the Bonnaventure, Grand and Petite Cascapedia, Dave Bishop I believe is guiding around there (I think he can be reached through the Gaspe Salmon Adventures operation). There are other rivers in the Gaspe, but I have no experience with them.