Once your business has a CRA business number, you can apply for the GST/HST number.
Sole Proprietorships need to call the CRA at 1-800-959-5525 to register for the GST/HST number, as well as other CRA business program accounts (import/export, payroll, etc).
Corporations can register for the GST/HST directly in Ownr in the “Organization” tab of the Ownr dashboard. The CRA payroll account can be registered at the same time.
The processing time for registering CRA business programs through Ownr is 1-2 weeks.
Alternatively, you can contact the CRA directly to register at 1-800-959-5525.
See this guide for further details.