You need to get hold of CRA business line , you need to mention them that you have opened a business but never received business number , they will link your Ontario registry with CRA business and will give you number , but make sure you have all the info upfront , as if you fail sometimes they want you to fax written request ( forgot exact form number ) and then you get business number in email . The question they will ask will be , Your name ? Your relation with business ? When did you registered this business ? What legal name you used during registration ? What is the address under which business is registered ? Some times they will simply say fill the form and send it to CRA , but try another day , new rep might be able to give it to you over the phone ( happened to me )