If you are looking for a complete list of the more than 850,000 Canadian postal codes, you may have to buy it. Canada Post does not offer a free-to-download list of Canadian postal codes. The list may be purchased by contacting GeoHelp Geography Division at 613-951-3889 or firstname.lastname@example.org.
If you are not looking for a download, a free list of Canadian postal codes can be found in the article "List of postal codes in Canada" on Wikipedia. The list can be sorted by province or alphabetically.
Additionally, if you just need to find a postal code for an individual address you can look it up at http://www.canadapost.ca/cpo/mc/personal/postalcode/fpc.jsf.