Canada splits income tax into two layers: a federal bracket table that is identical no matter where you live, and a provincial bracket table that each province sets independently. Ontario, British Columbia, and Alberta all use the same CPP and EI programs on the same national earnings bands, so for those three provinces, the entire gap in take-home pay comes down to the provincial brackets themselves, plus Ontario's two extra mechanisms: a two-tier surtax on Ontario tax payable, and the Ontario Health Premium, neither of which BC or Alberta have an equivalent of.
Alberta's brackets run from 8% to a 15% top rate with no surtax layered on, and its basic personal amount is the highest of the four provinces here, which is why it tends to net the most at moderate-to-higher salaries. British Columbia keeps its lower brackets quite gentle (5.6% and 7.7%) before stepping up more steeply past roughly $100,000 of taxable income, so it can actually outnet Alberta at lower salaries even though Alberta tends to pull ahead as income rises.
Quebec is a different case entirely. It isn't just a fourth set of brackets, it's a genuinely separate system: its own tax return via Revenu Québec, the Québec Pension Plan (QPP) instead of CPP, and the Québec Parental Insurance Plan (QPIP) charged in addition to a reduced federal EI rate. To avoid double-charging Quebec residents for programs the province runs itself, the federal government also reduces the federal tax Quebec residents owe by a flat 16.5% (the Quebec abatement). Even with that abatement, Quebec's combined provincial tax and payroll program costs are usually the highest of the four, which is exactly what this calculator shows.