The second unit's legal status decides how much of that rent even counts. A lender will only underwrite income from a suite the City of Saskatoon has permitted, so an unpermitted but occupied second unit can look profitable on paper while contributing close to nothing to what the property can actually be financed against.
The Residential Tenancies Act, 2006 governs any existing lease and transfers with the sale, so a buyer's lawyer should review both units' agreements before closing, since an existing tenant's below-market rent can drag down the actual cash flow for a year or more after possession.
Cash flow is a property-specific number built from its own rent roll and expenses, not a neighbourhood-wide answer. Get your hand-reviewed valuation from Joel Dyck.