See: https://www.cnbc.com/2017/10/16/airbus-teams-up-with-bombard...
It certainly isn't a payday for the Quebec government, but I suppose that 19% of something is better than 49% of nothing. One can _still_ criticize the irresponsible handling of taxpayer money AND now (if the manufacturing part is true) the benefits of the original buy-in will not go to Canadian factory workers.
The company they now own 50.01% pays the manufacturing and sales costs, so they're taking on that.
Using Airbus's Alabama factory will mean they can build/sell planes in the US and avoid 300% duty/tariff on those, and (according to the claims) "they'll secure more orders and double the value of the program" - which doesn't seem completely implausible...
Even if that's wildly optimistic, I'd guess even just farming out the 75 plane Delta order to Alabama and saving 220% and/or 300% in duty means a _lot_ of dollars (and cynically, if they were on the verge of losing the whole program, it'd be a super tempting lifeline to be thrown by Airbus...)