Start by gathering what only you hold. Permits, contractor invoices, the age of the furnace, the water heater and the shingles, whether the basement development was inspected, the utility bills, and photographs from before any renovation. The Saskatchewan REALTORS Association benchmark of $444,700 describes a typical home, and this pile of paper is precisely the material that separates yours from typical.
Then read your assessment notice for what it is. The City of Saskatoon assesses residential property using a percentage of value of 80 percent for taxation on a cycle that lags the market, so it was never intended to be a sale price. People compare it against an online estimate, notice they disagree, and assume the higher one must be the truth. They are two different measurements taken for two different purposes.
The valuation that means anything is the one that can show its work: the comparable sales, their dates, and the adjustments made for condition, lot and age. That is what Joel Dyck's hand-reviewed valuation puts in front of you, with the improvements no algorithm could have known about counted in the number.