A longer amortization lowers the monthly payment but stretches out how long you pay interest, which is the tradeoff behind why regulators cap it here rather than leaving it open-ended.
If your goal is a lower monthly payment on a Saskatoon purchase, the tools available are a larger down payment, a 30-year amortization where you qualify for uninsured financing, or comparing rates across lenders, not a longer term that does not exist in this market.
A mortgage broker can walk through which of those actually moves your payment the most for your situation. Get your hand-reviewed valuation from Joel Dyck.