The reality is for big projects quality should always be part of the contract. Use substandard quality materials and the whole contract is void.
The problem is that "agree on a level" and "lowest cost" are fundamentally opposite goals which require constant outside monitoring.
It's true that (a) workers must join a union when working on gov't projects and (b) The governing NDP is the "pro-union" party and thus, has received millions of donations from said unions.
The last part of what you wrote is worded poorly IMHO. Read literally, it seems to imply that donating to the party's campaign is part of the law itself. Which it isn't.
I agree, the effect is pretty much the same (due to (a) and (b) above) but I think it's important to clarify that point.
I’m not pro-union but unions aren’t the devil.
If you think corruption is bad in Quebec, look at BC. One of the first things our current government did was to pass a law requiring that all government-funded construction must be performed by workers belonging to unions which donated to the governing party's last election campaign. A short time later, they changed the procurement rules from "lowest cost bid" to "best bid", with the rules for determining "best" explicitly including how many jobs would be created for members of the aforementioned donor unions.