Here is the text for the Domestic Tariff
A. When Air Canada is unable to provide previously confirmed space due to there being more passengers holding confirmed reservations and tickets than for which there are available seats on a flight, Air Canada shall implement the provisions of this rule, except for employee and industry discounted travel.
B. Request for volunteers
(1) Air Canada will request volunteers from among the confirmed passengers to relinquish their seats in exchange for compensation, the amount and form of which will be at Air Canada’s discretion.
(2) Once a passenger has voluntarily relinquished his seat, he will not later be involuntarily denied boarding unless he was advised at the time he volunteered of such possibility and the amount of compensation to which he would be entitled.
(3) The request for volunteers and the selection of passengers to be denied boarding shall be in a manner solely determined by Air Canada.
C. Boarding priorities
(1) If a flight is overbooked, no passenger may be involuntarily denied boarding until Air Canada has first requested volunteers to relinquish their seats.
(2) In the event there are not enough volunteers, other passengers may be involuntarily denied boarding in accordance with Air Canada boarding priority policy. Passengers with confirmed reservations, will be permitted to board in the following order until all available seats are occupied:
a) Disabled passengers, unaccompanied children and youth under 18 years of age (having disclosed their age in the reservation) and others for whom, in Air Canada’s assessment, failure to carry would cause severe hardship;
b) Passengers paying Business (J Cabin) or Premium Economy (O cabin);
c) All other passengers, based on itinerary, fare paid status of loyalty program membership and the time in which the passenger presents herself for check-in without advance seat assignment;