For tax purposes, you need to keep your business records for six years.
Actually, the Canada Revenue Agency states that "if you file your return on time, keep your records for a minimum of six years after the end of the taxation year to which they relate" (emphasis added).
The CRA also cautions that if you have filed a tax objection or appeal, you should keep your records until the issue is settled, and until the time limit for filing any further appeal has expired (which may mean keeping records for a particular fiscal year longer than six years).
Note that if you want to destroy your business records before the six year minimum period is over, you need to get written permission from the director of your tax services office. The form to use for this is T137, Request For Destruction of Books and Records.