I am a non-resident of Canada — do I pay tax when I sell my Ontario home?

Yes. Non-residents of Canada who sell real property in Ontario are subject to Canadian income tax on the capital gain under the federal Income Tax Act. The gain is calculated the same way as for residents — proceeds minus adjusted cost base minus selling costs.

There is also a withholding obligation. The buyer is required to withhold a portion of the purchase price (typically 25% of the gross proceeds, or a negotiated holdback based on the gain) and remit it to the Canada Revenue Agency unless the seller obtains a "clearance certificate" from the CRA before closing. The clearance certificate process involves filing a formal notification, paying or securing the estimated tax, and waiting for the CRA to issue the certificate — this process can take weeks or months, so it should be started well before closing.

The principal residence exemption is available to non-residents for years in which the property was their principal residence while they were Canadian residents, but years of ownership as a non-resident generally do not qualify for the exemption. Ontario provincial income tax also applies to non-residents on Canadian-source gains.