You compared 50k nominal CAD and USD, rather than the same after exchange rate. Googling "50000 usd in cad" gives me $66,280 CAD; plugging that into your first link gives me an after-tax income of $53,317 CAD, which is $40,225 USD, a lot closer to the $38,888 Californian after-tax income.

More importantly, besides VAT (actually called GST in Canada) there's all the employer-side taxes that aren't advertised in a job posting. Try using the self-employment box in your Canadian calculator; for $66,820 CAD in self-employed income in BC, you end up with $48,229 CAD after tax, or only $36,378 USD on $50,000 USD.

That's not really fair or useful either, because the same situation will have all kinds of tax implications in CA as well. My point is more than simply looking at "this is what income tax is in jurisdiction A vs jurisdiction B" is not necessarily reflective of what the tax burden's actually like.