What happens if I'm a Canadian selling to a US buyer and the deal is priced in US dollars?

As a Canadian resident, you're still taxed on the sale in Canadian dollar terms regardless of what currency the deal is priced in. Your proceeds, and your cost base if it was originally recorded in a different currency, both need to be converted into Canadian dollars using the appropriate exchange rate at the relevant times, and that conversion is what actually determines your capital gain for Canadian tax purposes, not the US-dollar number written into the purchase agreement.

This creates a wrinkle that a same-currency deal wouldn't: currency movement between when the deal is agreed and when payments are actually received, particularly with deferred payments or an earn-out spread over time, can itself generate a foreign exchange gain or loss layered on top of the underlying business sale gain. If the Canadian dollar weakens or strengthens meaningfully between signing and each payment date, that shift shows up in your Canadian tax result even though the US-dollar price never changed.

Keeping careful records of the exchange rate at each relevant date, and working with an accountant experienced in cross-border transactions to calculate the actual Canadian-dollar gain (and any currency gain or loss), avoids under- or overreporting what you actually owe.