This is the new language on the website, which used to say credit valid until April 2021:

"If you made a flight booking for travel on or after March 1, 2020, and you want to cancel it, you can. The cancellation fee will be waived and you will receive full credit, which you can use towards future travel that must be completed within 24 months of the cancellation date. If you purchased a refundable fare and wish to refund it, a cancellation fee may still apply."

It is not for bookings made on or after March 1, it is the travel that was on or after March 1. It is clumsily worded, but given there is no alternate language for flights booked before March 1 I believe my read of this to be correct. Plus further down in the conditions it reads:

"Tickets must have been purchased directly from Air Canada, Kayak, Google Flights, Skyscanner or through your travel agent for travel on or after March 1, 2020."