Start with the City of Saskatoon's property file rather than the listing description or what the seller tells you, since the file shows the permit history, any inspection sign-offs and whether the zoning for that lot actually allows two units in the first place.
If the file comes back thin, that does not necessarily mean the suite has to be torn out, but it does mean a lender may not count its rental income. A home inspection, typically $400 to $600, is the fastest way to check whether the physical separation matches what the file says, and a lawyer should review what it would take to legalize it before that income goes into your offer.
A verbal assurance that everything is fine is worth exactly as much as the paper behind it. Get your hand-reviewed valuation from Joel Dyck.