The Articles of Incorporation are a legal document filed with a provincial or territorial government, or the federal government, which sets out a corporation's purpose and regulations. This is one of the documents necessary to the incorporation process.
When filed, the Articles of Incorporation create your corporation, and set out important matters such as the number of directors and types of shares a corporation will have.
If you are federally incorporating your business, this form is available from Corporations Canada by automatic fax, Internet, mail, or online. Corporations Canada is the branch of Industry Canada that administers the CBCA (Canada Business Corporations Act), and the office with which all filings, such as articles of incorporation, are made; there are offices in Vancouver, Ottawa, Montreal, and Toronto.
If you are provincially incorporating your business, you'll need to contact the appropriate Provincial Registrar. Some of these have Web sites, and you'll be able to download this form and others that you need. There are links to many of the provincial registries in my Incorporation Library.
This page of the Corporations Canada site shows a Sample Articles of Incorporation for a company with one class of shares.