If you are travelling within Canada, it is recommended to arrive at least two hours before your departure time. If you are travelling internationally, it is recommended to arrive at least three hours before your departure time.
Please note that the check-in counter hours are different for each airline. However, as a general rule, they close their counters at least an hour before boarding.
For more information, see the “When do the check-in counters open?” question in the “Check-in” section.