TORONTO--Porter Aviation Holdings Inc., the closely held parent of Porter Airlines Inc., said Wednesday it firmed up an order to buy up to 30 CSeries jets from Bombardier Inc., BBD.B.T +0.49% as the upstart regional Canadian airline looks to expand its service in North America.

The order had initially been signed as a letter of intent in December, but Porter asked Bombardier not disclose its identity. Wednesday, the companies confirmed that Porter will buy 12 of the 110-seat CS100 jets, the smaller of the two Bombardier CSeries jetliners, and take options for another 18.

In a statement, Montreal-based Bombardier said the order including options is worth $2.08 billion before discounts. It also said that, if Porter exercises its six purchase rights for Q400 NextGen aircraft, the contract value would increase to $2.29 billion, based on list prices.

Porter, which has a fleet of 26 Bombardier Q400 turboprops, is vying to become a national airline, cranking up the heat on much-larger rivals Air Canada AC.B.T +0.31% and WestJet Airlines Ltd. WJA.T -1.24% The all-new single-aisle jetliners will allow it to open up new routes.