The agreement also includes options for an additional 12 Boeing 787-10 aircraft.
The airline says it expects to start receiving the new aircraft in the fourth quarter of 2025 with the last one scheduled for delivery in the first quarter of 2027.
The order announced today substitutes an earlier deal for two Boeing 777 freighter aircraft.
Air Canada says the 787-10 is the largest model of the Dreamliner family and can carry more than 330 passengers depending on the seat configuration.
It also has 175 cubic meters of cargo volume.