Air Canada announced Wednesday it had placed a firm $6.5 billion order for 61 Boeing 737 MAX narrow-body aircraft, with options on 18 more planes and purchase rights for 30 others. The order -- which comes as the airline seeks to replace its aging Airbus A320 and A321 fleet -- concerns 33 of the MAX 8 version of the 737, and 28 of the MAX 9 aircraft.