The introduction of the Mitsubishi MRJ90 looms on the western horizon.
The MRJ-70 and MRJ-90 use a much narrower fuselage cross section, seating from 70 to 96 seats in 2x2 'Y' configuration. As such, the MRJ constitutes more of a threat to the Embraer E-Series, both CEO and NEO, which also have 2X2 configuration, but up to 130 seats in the stretched E-195 in LCC configuration.
The C Series, on the other hand, has a cross section significantly wider than either competitor - allowing 2x3 in 'Y' configuration (2x2 'J' configuration) and a seat count from 108 to 130 dual class, or 160 single class for the CS300 in a Ryanair style, single class layout.
The MRJ and the E-Jets are in a quite different market segment than the CS100 and 300.