Like most state-run or formerly state-run businesses in Canada, Air Canada has its HQ and as many functions, such as engineering, as they can manage, in the French-speaking part of Canada. It's the Canadian political way. It's just an inconvenience for them that far more passengers want to route through Toronto.
You will notice when flying with them what a high proportion of the flight deck crews have French-Canadian accents, even on the Western Canada transatlantic routes.