SEDAR provides access to most public securities documents and information filed by issuers with the thirteen provincial and territorial securities regulatory authorities ("Canadian Securities Administrators" or "CSA"). Files go back to 1994.
The U.S. Securities and Exchange Commission (SEC) makes all submissions by U.S. public companies since 1993 available in full-text.
Don't forget to check the website for the company you are researching. Look for links to newsletters, press releases, or other communication outlets that provide information about the company. Many public companies also post their recent annual reports on their website.
Western Libraries has an extensive collection of historical annual reports and financial statements primarily for Canadian companies, but the collection does include US companies as well. Contact the Business Library if you are interested in obtaining a copy of any of the reports.