I believe the stamping on the shackle likely reads “SPRINGER”. There was a Springer Lock Mfg. Co. Ltd. located in Bellville, Ontario, a pdf copy of their Catalog No. 3, ca 1920 can be found at the link and their padlock offerings from the era on pg. 424-425:
Thanks Pete, on closer inspection with a strong light, namely the sun, I was able to make out part of what could and probably is an “R” after the letters “SPRINGE”.
The Dominion Power and Transmission Company is also a good possibility as both were Canadian companies and it got it’s name in 1907 and in 1930 became part of what is now Ontario Hydro.
Also I have a “DRAGON” pancake padlock that also has the number 15 on the reverse of the shackle.
Coincidence?