The CSeries is more of a wildcard than the SSJ! It might not even be ready to fly by the time WX are ready to start their fleet renewal. Not to mention the complete lack of real world data with respect to performance vs manufacturer's specs...
Interjet seem to have had good success with the Superjet and I suspect there will have been quite a few phone calls between Cityjet's Head Office and Mexico in the past months. The SSJ is built with far more Western engineered components than previous iterations of Soviet aircraft, it's more of a case of overturning perception in the way the Skoda had to 20-ish years ago.