Does a realtor selling a power of sale property represent the lender or the original owner in Ontario?

Generally, a realtor engaged to sell a power of sale property is retained by, and owes their representation duties to, the lender that is exercising its mortgage security - not the original homeowner who defaulted. This works the same way agency generally works in any listing arrangement: the realtor's client is whoever retained them for the transaction, and here that is the lender standing in the seller's position, regulated in the usual way under TRESA through the Real Estate Council of Ontario.

For a buyer, the practical takeaway is that the listing realtor's obligations run to the lender's interests in achieving a sale, not to protecting you as the purchaser, which is really no different from how any listing agent's role works in an ordinary transaction. It also reinforces why having your own representation, and ultimately your own lawyer, matters just as much here as it would buying from an individual seller - arguably more, given how limited the lender's own representations about the property tend to be.

Make sure you have your own realtor and lawyer looking out for your interests, rather than relying on the listing realtor to do so.