Is a signing bonus taxed differently than my regular salary?

Not in the end — a signing bonus is ultimately taxed at exactly the same marginal tax rates as your regular salary, once your full year's income is calculated. There's a common misconception that bonuses get hit with a special, higher "bonus tax rate," but that's not how the actual tax owed is determined; a bonus is just additional employment income added to everything else you earned that year.

What does look different, and what fuels this misconception, is how much tax gets withheld from the bonus paycheque itself. Employers commonly apply higher withholding to a lump-sum bonus payment because of how CRA's payroll withholding formulas work for irregular or lump-sum payments — the formula effectively assumes you'll receive that same higher amount every pay period, which pushes up the withholding rate on that specific cheque even though your actual total income for the year hasn't changed based on that assumption.

The practical result is that a bonus paycheque often looks much more heavily taxed than a regular one, which understandably frustrates people, but the extra amount withheld isn't lost — it's reconciled when you file your return, either as part of your refund or reducing what you owe, based on your real total income and real marginal rate for the year.