Air Canada's flight change policies may vary, and it's always best to check directly with the airline or visit their official website for the most up-to-date information. As of my last knowledge update in 2023.

24-Hour Risk-Free Cancellation/Change Period:
Many airlines, including Air Canada, typically offer a 24-hour risk-free cancellation or change period for flights booked directly with the airline. During this period, you can make changes to your reservation or cancel it without incurring any change fees or penalties.
Booking Conditions:
The ability to make changes without fees may depend on the fare type and the conditions of your ticket. Some discounted or promotional fares may have more restrictive change policies.
Online or Contact Center:
Changes within the 24-hour period can often be done online through the airline's website or by contacting their customer service. If you booked through a travel agency or third-party website, you might need to contact them directly for changes.
Same-Day Flight Changes:
Air Canada may offer same-day flight changes for a fee, allowing you to switch to an earlier or later flight on the same day. This is subject to availability and specific terms and conditions.
Flight Flexibility Options:
Air Canada may offer flexible fare options that allow for changes with reduced fees or additional benefits. These options may vary, so it's important to review the specific terms associated with the fare you choose.