A third unit adds a rent roll but also adds complexity: more egress and fire-separation requirements from the City of Saskatoon, more tenants under the Residential Tenancies Act, 2006, and usually a larger down payment since lenders treat a non-owner-occupied multi-unit differently than a duplex you live in.
The legality question decides the real value gap. An unpermitted suite in either configuration is income you cannot advertise honestly, insure properly, or count on when you resell, and it will not show up correctly on any public-record estimate.
Joel Dyck prices multi-family property against the building's actual, verified condition and legal suite count rather than the listing description. Get your hand-reviewed valuation from Joel Dyck.