The math depends on whether the second unit is legal. The City of Saskatoon requires a secondary suite to meet zoning, fire separation and egress rules, and a lender will only count rental income from a unit that is properly registered. An unpermitted suite can still house a tenant, but it will not help your mortgage application.
A first-time buyer also has to manage being a landlord from day one, which means budgeting for vacancy, maintenance and tenant turnover on top of the mortgage, plus a home inspection running $400 to $600 before closing. That workload is real, and it should be weighed against the income benefit rather than assumed away.
Joel Dyck can pull comparable two-family sales in Fairhaven and confirm suite legality before you make an offer, so the income projection you're relying on is real. Get your hand-reviewed valuation from Joel Dyck.