In the early 1960's I worked at Denison Mines in Elliot Lake, Ont. Once I borrowed $50.00 from a guy, whose only occupation on the mine camp was loan sharking. He demanded back the double amount at next payday, which was two weeks away. I paid the bastard, and NEVER again did I do anything with slime like that, again legal or otherwise.
Nowadays, I don't even wait for my credit card bill to arrive in the mail. I am online, and use my credit card for everything, because at the end of the year I get back 1% of all previous year's purchases. I pay the billed amount on time and in full.
There is a word in American English (don't know if it is used in Canada): VIGORISH. That is the name of re-payments loan sharks demand.