How long do these documents need to be retained for?
You must keep your important documents for a minimum of six years after the end of the last fiscal year they refer to. Nonetheless, we recommend you to keep them for at least ten years since previous documents can prove to be very useful if you need verification.
Visit the following website for more details:
http://www.revenuquebec.ca/fr/entreprise/impot/societes/documents.aspx