I've fished with Brad Petzke for Atlantics.
He does not fish the rapids as you have to have a Canadian license for that.
He fishes the power houses.
Had a great time, caught a bunch of Atlantics, a steelhead or two and a bunch of whitefish which we kept and boy they do taste goood!
Beware that the fishing for atlantics to be successful involves a couple of different techniques all out of a boat.
Nymphing under a indicator, nymphing with just a straight line, casting and stripping back streamers, dead drifting "unconventional" streamers, trolling streamers and stripping streamers at the same time and hopefully you'll see some atlantics busting the surface after bait fish. When they are busting the surface its a hoot, The guy I was with hooked 3 fish on one cast while they where busting the surface. I'd say that there is almost nothing as exciting as seeing your streamer laying in the water 10 ft from the boat, twitching it and having a 10lb atlantic smash the crap out of it.
Brad knows his stuff on the Atlantics in the St. Mary's, just be aware its not your typical fly fishing.