In his article on Seaway Administrator Collister Johnson's comments, Marc Heller states that "the Seaway was not open to ocean freighters until 1959."
While the Seaway as we know it was opened in 1959, prior to that a series of canals allowed small vessels, approximately 250 feet in length and drawing 14 feet of water, to bypass the rapids in the St. Lawrence between Prescott, Ontario, and Montreal.
While the traffic was primarily domestic, this system also enabled a significant amount of foreign-flag tonnage to access to the Great Lakes through the St. Lawrence corridor.
Robert Graham
Massena