There are lots of places to park along the CDN or USA side of the St. Lawrence.
Here is some info on ones we have used. We like to use a base camp and do a lot of side trips. We stayed at the Massena CG for a couple of weeks and took side trips in just about all directions within 75 miles of the CG.
http://fasteaglervparking.blogspot.com/2015/09/messena-international-kampground.html
http://fasteaglervparking.blogspot.com/2015/06/coles-creek-state-park-waddington-ny.html