A .ca domain name can be registered for a minimum of 1 year to a maximum of 10 years. It can be renewed at any time during this period but at any given time the total registration can never exceed 10 years. For example if you want to register a domain for 20 years, you must register it for 10 years and before expiration renew it for another 10 years. As long as you renew your domain name you can keep it as long as you want.
Auto-Renew Grace Period
Upon its expiry, the domain name go through the "Auto-Renew Grace Period". It's usually during this period that the Registrar automatically renew the domain according to prior agreement with the Registrant. If no renewal agreement has been established between the Registrant and the Registrar, the Registrar may or may not disable or delete the domain name. The main reason to disabling the domain is to draw attention to the Registrant. A deleted domain go directly to the "Redemption Grace Period".
Redemption Grace Period
The Redemption Grace Period still allow the domain to be renewed or transfered but the domain name is now suspended/disabled, any web site or email associated with it will not work.
TBR (To Be Released)
If a domain name is not redeemed during the 30 days "Redemption Grace Period", the domain moves to the TBR status. Before going back to public availability, expired domains go through a "TBR Session" where Registrars can or not compete to get theses domains. The TBR session happens only once a week, every Wednesday at 2:00 PM (Ottawa time). A domain name stay between 60 hours and 7 days in TBR status until the opening of the next TBR session. If the domain is not claimed during the session, it becomes available to public registration.