I booked a round trip flight to an international destination in December on Air Canada's website for a flight at the end of April. In February I received an e-mail from Air Canada advising of their low price guarantee offering a refund of the difference if there was a cheaper flight offered on any other travel website. I checked and found two cheaper flights, by about $170 (or 10%) a ticket.
When I submitted a claim I was told that the program applied only if you submit a claim within 24 hours of booking on the AC website. When I pointed out the introduction of the program only in February they advised the program has existed since 2009 as the "Lowest Fare Guarantee" BUT it was "re-launched" with a branding change and also "expanded to include international itineraries". My flight is international so I presume that the program did not exist for it when I booked in December.
Lessons learned: 1. Check prices as third party suppliers can apparently sell Air Canada flights cheaper than Air Canada can. 2. Don't rely on Air Canada's customer service to help if you have a problem.