A legal two-family property, one where both units are permitted through the City of Saskatoon, generally finances and rents more predictably than an informal arrangement, because a lender and an eventual buyer can both verify the second unit rather than taking your word for it. That legal status changes both your financing options and your resale value, sometimes more than the extra rent does.
To estimate a real return, add both units' realistic rent, subtract the mortgage payment, property tax, insurance and a maintenance reserve, and compare what remains against your actual cash invested, including any CMHC-insured minimum down payment, 5 percent on the first $500,000 of the purchase price. Two nearly identical Mayfair two-family properties can produce different returns purely because of financing choices.
The number that matters is the one built from your actual purchase price and financing, not a percentage borrowed from a different property or a different market. Get your hand-reviewed valuation from Joel Dyck.