I'm a Canadian that has worked in a few large, unionized public or quasi-public workplaces as an engineer. In general hours of work, benefits (extended medical / dental) and vacation / sick leave will be better than in non-union private sector workplaces. Salaries tend to higher at the entry-level and comparable at the high end.
However, I have always found employee satisfaction and employee-management relations to be far worse in the large union workplaces.
I believe it is due to the fact that having a big, strong union that is capable of basically strong-arming the employer through the threat of job action (if you operate a nuclear power plant, having your engineers go on strike is not really an option) forces management to concede benefits they don't truly believe employees deserve, and that leads to clawbacks of, well, pretty much everything that isn't in the collective agreement. So you might get your 18 sick days (which you can never use without lying because no one who is not chronically ill gets sick for 18 working days every year), but you might have to fill out a multi-page form to get a new notebook (a paper notebook not a notebook computer).
Look at the sort of treatment that contract or temp employees get in big unionized workplaces - generally awful, and that reflects the company's true attitude toward it's employees.
I'd much rather work in a non-union workplace where I get benefits above the statutory minimums because the company truly values it's employees and understands that people who are treated well are more productive than one where everything I get was a concession to avoid labour strife.
If non-unionized company X gives 3 weeks paid vacation per year (2 weeks is the mandatory minimum in Canada) because they want to, that's much more likely to translate into a great workplace than the 4 weeks company Y gives because their employees are members of a massive national labour union and demand it.
Just my $0.02 from personal experience.