Once your business has a CRA business number, you can apply for the GST/HST number.
How you get the GST/HST number depends on the type of business you have:
Sole proprietorships
To register for GST/HST for your sole proprietorship, follow the instructions on the Register for a GST/HST account page. You can also register for other other CRA business program accounts (import/export, payroll, etc).
Corporations
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 register directly with the CRA by following the instructions on the Register for a GST/HST account page.
See this guide for further details.