An early St. Lawrence Seaway expands protected war production

How would completing the St. Lawrence Seaway before 1939 affect the Second World War and Great Lakes industry?

It would enlarge protected industrial and training capacity around the Great Lakes and simplify movement of aircraft and other matériel between the United States and Canada.

The Seaway would make more shipbuilding and training possible far from enemy action while strengthening the regional industrial base. It could also replace awkward border-transfer arrangements with barge and water transport for aircraft and other supplies.