This image shows a view of the lock door for the Canadian Lock on the Canadian side of the Soo Locks.
“Plastichrome” by Colourpicture., Boston 15, Mass., U.S.A.
The description states:
THE CANADIAN LOCK
As seen from the observation deck of the Diesel operated vessel “Messenger”. Opened in 1895 by the Dominion of Canada, the Canadian Lock is 900 feet long, 60 feet wide, 17 feet deep with a lift of 22 feet. Cost $2,500,000. A majority of the passenger boats use this lock.
–The lock has been deactivated and is part of the Sault Ste. Marie Canal Historic District. At its construction, it was the first electrically operated lock in the world.
This card likely dates from the 1950s.