Under what circumstance would the U.S. dollar and the Canadian dollar be said to have achieved purchasing power parity?

The U.S. dollar and the Canadian dollar possible considered to have achieved purchasing power parity when the exchange rate reflects the relative prices of a market basket of traded goods and services at the current exchange rate.  There probably no incentive to convert U.S. dollars to Canadian dollars nor to exchange Canadian dollars to U.S. dollars and buy goods or services in the other country.