Do some Ontario municipalities require a rental licence for multi-unit buildings, and does it transfer on sale?

Yes, some Ontario municipalities require landlords of certain rental properties, often multi-unit buildings specifically, to hold a rental licence under a local bylaw, generally tied to standards around safety, maintenance, and occupancy. Whether a specific property is subject to this kind of requirement, and exactly what the licence involves, depends entirely on the municipality where the property is located, since there is no single province-wide rule.

Where a licence is required, it generally does not automatically transfer to a new owner along with the sale; you may need to apply for your own licence, and in some cases undergo an inspection, before you are considered compliant as the new landlord. Buying on the assumption that an existing licence simply carries over is a real risk, since a gap in licensing can expose you to bylaw enforcement even if the previous owner was fully compliant. Confirm directly with the municipality what licensing applies to the specific property and what you need to do as the incoming owner before or shortly after closing.