The mortgage payout is where estimates go wrong most often. Call your lender for a written payout statement, because breaking a fixed rate mortgage early can trigger an interest rate differential charge that is far larger than three months of interest, and a home equity line of credit registered against title has to be discharged as well. Your lawyer handles the discharge through Information Services Corporation.
Then the adjustments. Property taxes are apportioned between you and the buyer to the possession date, so a seller who has prepaid the year is credited and one who has not is debited. Add moving costs, any repairs you agree to after the buyer's inspection, and utility final readings. For a condominium, an estoppel certificate and any special assessment need to be settled too.
Tax is the last question. A principal residence is generally exempt from capital gains tax, but the Canada Revenue Agency still requires the sale to be reported on your return, and a rental or a second property is a different calculation. All of it rests on the sale price being right in the first place, which is what Joel Dyck's hand-reviewed valuation establishes.