Around the islands that make up the greater Montreal area there are various decent swing waters but not clean. A wide variety of species available but all warm water fare.
The Saranac and Boquet are great in NY and the Salmon in Pulaski is good if you go to the controlled fly fishing beats. Otherwise too crowded to swing even a 40 foot radius. There is also the Salmon in Malone NY.
The lower sections of the Diable in mont Tremblant and the Rouge in and below Harrington down to its mouth with the Ottawa river can offer big enough water for warm species and trout but in relatively nice rivers.
The Chateauguay river starting in NY runs through Powerscourt and Athelston for some nice browns that are fussy but more of a 5wt and under river.
There are a few good rivers out towards Quebec City and Trois-Rivieres but I don't know them well ( yet to explore ).
You can check out the Nicolet and some sections of rivière du Nord could be swung near st Jerome.
You won't find anadromous runs anywhere unless you drive 7 hours out to the Matane or st John or better yet the Gaspe.
If your fixing on anywhere in particular following your research, shoot me a pm and I'll give you what details I know of where you are heading and if I know the river well, I'll join you
Considering our mayor just dumped a few million tons of sewage into the st Lawrence, a lot of anglers have been turned off. There is an American shad run on the north side of the island in the spring but it's really crowded. There is also st. Anne de Bellevue that can be waded and swung at low-water conditions. The lachine Rapids as well as the bird sanctuary island offer some swing areas as well and I'm sure there are plenty of other spots I haven't discovered yet.
I always have this distaste for fishing the st Lawrence however last three seasons I've given it a few more chances and had some surprises.
There is also another part in lasalle with some decent access that could be swung, and there's a nice little section near my house in pierrefonds that has plenty of action in the high summer months.