The math only works if the suite is legal. A permitted secondary suite has documented egress windows, ceiling height and fire separation on file with the city, and a lender who sees that permit will underwrite the rental income as part of your qualifying income rather than ignoring it.
An unpermitted suite can still generate rent, but a lender generally will not count that income toward affordability, which defeats the purpose of buying the extra unit in the first place. That gap between what a suite earns and what a lender will credit is exactly what an automated online estimate cannot see.
For a buyer stretching to afford Saskatoon's $444,700 benchmark price, a legal second unit can be the difference between qualifying and not. Get your hand-reviewed valuation from Joel Dyck.