The GST/HST/PST is not the same as a business number (please visit, What are GST, HST, and PST? for more information). BN, or Business Number, is a unique, nine-digit number and the standard identifier for businesses, which is unique to a business or legal entity. The BN is issued by the CRA to businesses and sole proprietors and used as a standard identifier for your business.
If you do not have a BN, you can get one online on the Government of Canada website here.
Need to set up your tax information? Go to: How to complete payment and tax set up.
Need to edit your tax information? Go to: How to edit tax and payment set up.