The order, first announced in February, is valued at about $3.8 billion, the companies said in a statement.
It would increase to $6.3 billion if the airline, Canada's largest, exercises its option to buy the 30 additional jets.
The companies said deliveries were scheduled to begin in late 2019 and extend to 2022.
The order was the first in 16 months for the CSeries aircraft, which has been plagued by delays and higher-than-expected costs, and is a major boost for Bombardier.
The planemaker last week signed a long-expected deal with Quebec for the Canadian province to invest in its CSeries jets and is also in talks with Canada's federal government over possible investment, a deal that is proving harder to pull off.