Which province's tax rate do I charge a client who gives me two different addresses in two provinces?

When a client has addresses in more than one province and it isn't clear which one the supply relates to, the GST/HST place-of-supply rules include specific tie-breaking criteria designed to land on a single applicable province, rather than leaving the choice up to whichever address happens to be listed first or most conveniently. These rules generally work through a set sequence of factors, looking at things like which address most directly relates to the particular supply, until one province is identified as the correct answer.

This is different from simply picking whichever address the client uses for billing, or defaulting to whichever province charges less tax, both of which can lead to charging the wrong rate. The right approach is to work through the applicable factors for the type of supply involved and the actual facts of the engagement, rather than guessing or asking the client to simply choose a preferred province.

Because the tie-breaking rules can be detailed and vary depending on what's actually being supplied, and an incorrect rate creates exposure regardless of which way the error goes, don't resolve a two-address situation informally, confirm the correct province with a tax advisor for that specific client and engagement.