C-Series offers Comac a cheap & practical solution.....Pure speculation on my part here so don't take this too seriously, but doesn't Bombardier already have a fairly elaborate agreement with Comac about sharing some of the technologies developed for the C-Series.
An opportunity for Comac to fast track its own developement programs, plus they've stated their business plan is to compete directly with Boeing and Airbus. Funding for the CS500 development costs provided also.
Wouldn't politicians look good if it was announced that a deal between Bombardier & Comac was reached, with the blessing from all governments with new job sharing between both countries.
I won't hold my breath here, but from what I do understand, the context, why not?