ConfigurationsAny larger jet can be configured to a lower capacity. However, whether it remains competitive in that configuration is debatable and probably depends on a lot of other factors.
Generally speaking larger jets aren't economical when flown half-filled, or configured to a much lower number of passengers than was originally intended in the design of the aircraft.
Embraer's E-190/195 has a capacity of between 100-to-120 passengers. C series seats between 100 and 130 passengers. C Series is a more technologically advanced aircraft. It is lighter, cleaner, quieter, and much more fuel efficient.
The narrowbodies Airbus and Boeing build generally start around 150 seats. Of course they can be configured to smaller capacities - which gives each passenger much more room - but in a world of heavy competition from the low-cost carriers that approach doesn't seem to appeal to many carriers. Most are moving in the other direction by cutting costs to the bone, and offering even more pared down services, or none at all.
Media loves to perpetuate the myth that C series is trying to compete against Boeing and Airbus and failing in the process. C series has the potential to compete with Airbus and Boeing only if Bombardier decides to stretch the design.
But to suggest that an aircraft with a seating capacity of 130 competes head-to-head with aircraft seating 150 isn't practical. Of course, all aircraft compete. In the broadest sense we could say that RJs compete with Airbus380s, but generally when we talk about aircraft competing with each other we talk about aircraft of the same passenger carrying capacities.