Replacing a widebody jet on a premier long-haul corridor with a single-aisle aircraft sounds like a masterclass in fuel efficiency, but Air Canada quietly abandoned that exact strategy before the first passenger even boarded. When schedule filings initially showed the carrier deploying its brand-new Airbus A321XLR on AC852 between Toronto Pearson(YYZ) and London Heathrow(LHR), it appeared to begin the evolution with which North American network carriers would manage top-tier transatlantic trunk routes. Within months, however, Air Canada pulled the narrowbody from the schedule, restoring twin-aisle Boeing 777 and 787 Dreamlinerservice to protect high-density seat inventory and premium belly-freight capacity.