United Airlines is poised to order another $2 billion of Boeing Co.’s narrow-body jets, snubbing newer models from Canada’s Bombardier Inc. and Brazil’s Embraer SA for the second time in a little more than a month, according to two people familiar with the airline’s plans. The third-largest U.S. carrier is planning to add 25 of Boeing’s 737 jetliners after studying Bombardier’s C Series and Embraer’s offerings in the 100-seat category, the people said. United announced a $3.22 billion order for 40 of the Boeing aircraft with its quarterly earnings in January. United has been stocking up on 737s, the mainstay of its domestic fleet, as the airline phases out cramped 50-seat regional jets from shorter routes. The carrier now operates 310 737s, Boeing’s best-selling product. Representatives of the companies declined to comment on the latest fleet move, which was reported first by the Wall Street Journal. United has stuck with updated versions of the 737, which debuted in 1965, instead of adding Bombardier’s brand-new C Series, which has struggled to gain a foothold in the U.S. despite boasts of fuel and maintenance savings. The Canadian planemaker scored a sales breakthrough earlier this month when Air Canada announced its intent to order as many as 75 of the jets.