As I said, the C-Series sits beneath the entrenched market that Airbus and Boeing compete in - the fact that the CS300 touches the low end of Airbus and Boeings products capacity wise doesnt alter that, as airline orders have been trending toward the top end of those offerings for several years.
A319NEO orders stand, to date, at just 55, with the bulk of Airbuses orders going to the A320NEO (two thirds at 3,600) and A321 (a third at 1,400).
737MAX orders are trending a similar way where airlines have identified the subtype, with the 737 MAX 7 only seeing 60 orders to date, with the rest of the orders split in a similar way to that of the Airbus products.
The C-Series simply doesnt compete in the same market.
As to a CS500, sorry but its a pipe dream. Bombardier have enough debt and issues with the CS100 and CS300, they simply cant commit to a new stretch in the next decade. They also dont have enough orders currently to break even on the current versions, and don't have an engine for anything larger so that would need more investment with an engine company.
There is also no evidence of strong arming by Airbus and Boeing - yes, Bombardier approached Airbus for investment and were denied, but neither Airbus nor Boeing have anything to gain by stopping Bombardier compete at the low end of the market. Bombardiers main competitor is Embraer and the new jets coming out of Russia (Sukhoi Superjet), China (Comac C919 and ARJ19) and Japan (MRJ). Airbus and Boeing dont want to compete in the regional jet market.