The detail that trips up a lot of buyers is compounding. Canadian mortgages compound semi annually rather than monthly, unlike the monthly compounding a foreign calculator assumes, so lenders here apply the correct Canadian formula automatically rather than the simpler one.
If your down payment is under 20 percent, the CMHC, Sagen or Canada Guaranty insurance premium gets added to the principal before the payment is calculated, so the number you see already includes it rather than showing it as a separate line.
Property tax and, on a condominium, part of the monthly fee are often layered on top of the mortgage payment itself in a lender's overall affordability figure. Get your hand-reviewed valuation from Joel Dyck.