From July 1st 2021, a GST/HST tax will be added to invoices of Google Ads, Google Marketing Platform & and other customers with a billing address in Canada that are billed out of Google LLC. No taxes will be collected from business customers that provide a GST/HST registration number. In the absence of this tax ID, Google LLC is required to charge the tax amount, therefore to ensure taxes are collected correctly, customers must provide Google with their GST/HST registration number (if they have one).
If you do not have a GST/HST Registration Number no action is required and the appropriate tax amount will be automatically applied to their invoices starting from July.
A call to Google Ads support stated that if you are tax exempt, then you can leave this area blank.
Also you can always contact Google Ads Support to verify any information regarding these recent updates for Google Ads and Canadian Tax updates.
Ultimately contact your own tax adviser for any questions regarding this.