Looks like United has decided against the CSeries, E2 for their second order:
Boeing Beats Out Bombardier, Embraer for Coveted United Orders -- Wall Street Journal
United Continental finalizes second deal with Boeing for new single-aisle jets
By JON OSTROWER
Boeing Co. is finalizing a new deal to sell its single-aisle jets to United Continental Holdings Inc. that would enable the U.S. aerospace giant to block smaller rivals Bombardier Inc. and Embraer SA, from gaining a coveted spot in the airline’s fleet, according to people familiar with the negotiations.
United is expected to order 25 Boeing 737s in the newest deal, the people said, after an earlier deal in January to buy 40 737-700s.