Unlike other cheques, Government of Canada cheques never expire and can be cashed at any time. CRA can issue replacement cheques if the original was lost, destroyed, stolen or missing.
However, note that CRA is moving towards using direct deposit for all payments it issues. You may be able to use different account information for certain types of payments.
For more information on direct deposit, see http://www.cra-arc.gc.ca/directdeposit/.