This is one of four guns that were the principal armament of the Canadian Fisheries Protection Service vessel CGS (Canadian Government Ship) Canada. 

As part of the Fisheries Protection Service, Canada patrolled the east coast against American civilian ships fishing illegally in Canadian waters. This did not require heavy armament, and so Canada received four of these relatively light automatic weapons. Essentially scaled-up machine-guns, they were often called "pom-poms" because of the noise they made when firing.

Naval Gun, 1 1/4 - Pounder, Automatic
CWM 19440021-001