Friend, you have some great options in the St. Catharines area! Don't be discouraged by the lack of replies to this thread. I get the impression that more users are in the GTA. I'm living in Etobicoke but St. Catharines/Niagara is my home turf!
How do you like to fish? What for? Here are some places to get started. None of them are specific, so you might need some briefing in the bigger watersheds.
1) Port Dalhousie (in the current) for Salmon, Rainbows, nice Browns, and walleye OR fill your boots with sheepshead in the summer. Even caught some eels!
2) Port Dalhousie harbour for large northerns, nice bass, and cruising trout. Walleye also along the breakwall.
3) Port Dalhousie pier (E or W) for early autumn salmon w/ spoons dusk/dawn/night
4) Whirlpool or Queenston Docks in the Niagara River.
5) Lock 1 if its still open... might've fenced that off since I was there a few years ago
6) The beaverdams road area for perch, bass, sunfish
7) Cast for pike in the Henley (now) south of the highway bridge
8) Sixteen mile creek for largemouth and carp
9) If you have a boat, the Queenston drift or mouth of the Niagara out by the green can can be stellar (be careful which side or you'll need a US licence! Seriously! Same goes for the river!)
10) Downrigging along the Niagara Bar for lakers is fun on those hot summer days with flat water. There's plenty of salmon fishing to be had as well, but I haven't done that for a few years.
11) Up by Brock I hear there's somefishing but I don't know it well.
12) The upper Niagara river (N of Ft. Erie) I've been scuba diving and seen some HUGE bass, walleye and trout. It's also been featured in magazines. Well earned reputation. Same goes for Chippewa creek.
13) You're a short drive for very very early morning Lake Erie breakwall walleye.
14) GM backwash used to have Salmon but that's been >10 years since I've tried.
15) Catfish in the 4 mile creek near Virgil, NOTL.
16) Niagara Jetboats closed the sand docks but I've seen Sturgeon, nice salmon and trout, very very big walleye, musky and others caught right down there. Shore fishing is tricky due to the steep banks but there are a few accesses.
You should go see Angela at Peter's Tackle & Bait on Secord Drive (between Lake St. & Scott St.). She runs the store now - you'll like her and she knows her stuff. (incidentally, the store is named after her late husband, Peter - an awesome guy who passed away several years ago).
These should give you some leads on where to get started. PM me with specific questions about locations or the 'how's'.
Cheers,
M