Postal orders were a service provided by the Canadian Post Office, and was a method of transferring funds between 1898 and 1 April 1949.
Postal orders have been issued by the Canadian Post Office roughly since confederation (the timeline linked to below, for example, cites the postal money order system as expanding to Manitoba in July 1873).
Money orders were issue for values up to $100, while postal notes (introduced 4 August 1898) were for sending small sums between 10¢ and $5.
Canada was the only British Commonwealth country to issue special postal note stamps.
In July 2006, a set of 3 British postal orders overprinted "Canada" and the word "Specimen" turned up and were sold on eBay for £7,123.