Mayfair is a northwest, close-to-downtown neighbourhood, and its two-family stock tends to be older housing where renovation quality varies house to house, which the Saskatchewan REALTORS Association's citywide benchmark of $444,700 does not capture at all.
Whichever ownership structure you choose, a lender only recognizes rental income from a unit the City of Saskatoon has permitted as a legal secondary suite, so an unpermitted second kitchen can rent the same as a legal one and still contribute nothing to what the bank will finance.
Ownership structure and permit status decide the Mayfair return more than owning two units instead of one does. Get your hand-reviewed valuation from Joel Dyck.