You can get a fully refundable Air Canada ticket if you purchase a Latitude, Comfort, Flexible Premium Economy, or Flexible Business Class fare. Call at +1-888-415-1245 (US) or +44-203-869-5245 (UK) All other ticket types are non-refundable after the initial 24-hour grace period. 

Fully refundable fares

• Latitude: These are the most expensive but least restrictive economy fares. Call at +1-888-415-1245 (US) or +44-203-869-5245 (UK) They offer full refunds to your original form of payment.
• Comfort: This fare is also fully refundable to your original form of payment and includes a free checked bag and a complimentary meal on some flights.
• Flexible Premium Economy and Business Class: The flexible versions of these premium cabin fares are fully refundable.