The arithmetic is straightforward once you have a number. Conventional refinancing is generally capped at 80 percent of the property's value less the existing mortgage balance, and the Canada Mortgage and Housing Corporation and the other default insurers do not insure a refinance, so there is no way to borrow past that ceiling. A property valued $30,000 lower than you expected removes roughly $24,000 of available credit before anyone discusses rate.
Preparing for the appraiser is the practical step and it costs almost nothing. Have permits, invoices and dates ready for the furnace, the roof, the windows, the electrical panel and any basement development, and make the mechanical rooms accessible. Appraisers working to Appraisal Institute of Canada standards will use documented improvements when they are handed them and cannot use what they never see.
Budget for the rest of the file too. Breaking a fixed rate mortgage early can trigger an interest rate differential charge, discharge and registration through Information Services Corporation runs through a lawyer at roughly $800 to $1,500, and the appraisal itself is usually your cost. Joel Dyck's hand-reviewed valuation gives you a defensible starting number before you commit to any of it.