While Boeing and Airbus long ago ceded the sub-100 seat market to Bombardier and Embraer, this new aircraft is going to compete head-on with the lower end of the Boeing and Airbus markets. The aircraft will hold 110 to 130 people.
As I've discussed here before, the C-Series is planning to use the Pratt & Whitney Geared Turbofan which will give the plane substantial improvements in fuel economy . . . if the engines can actually deliver. They seem to still be sticking to their aggressive 20%+ increase in fuel economy promise. The in-service date for this plane is scheduled for 2013, and that's a good 5+ years before Airbus and Boeing expect to have a replacement available for their current narrowbodies.
This is an extremely risky venture for Bombardier. It's highly unusual for an aircraft to be launched with absolutely no firm orders. The only thing they have right now is a "letter of interest" from Lufthansa for 30 planes plus 30 options. That hardly sounds solid, but I'm sure I know why they did it. If this plane can live up to the economics that are being promised, well, it's going to see a flood of orders.
Whether these ambitious goals can be met remains to be seen. By delaying a replacement for the 737 and A320 series aircraft, Boeing and Airbus have left the door open for someone else to move in. Can Bombardier pull it off?