For Air Canada, the check in can happen in three different ways: web, mobile and at the airport.
The web check in begins 24 hours before the departure of flights and up to 45 minutes before departure of flights within Canada and 60 minutes before flights between Canada and other countries. It is permissible on Air Canada and Air Canada Express (operated only by Jazz). You are allowed to print the boarding pass using web check in facility.
You would need an Aeroplan number or the booking reference number along with your passport and address in USA.
There are a number of options provided using the web check in. These are of
Web check in allows 9 passengers to check-in in one session.
Mobile check in is also available to the passengers. This can be done by visiting mobile.aircanada.com from your mobile device. Alternatively, you can download the Air Canada mobile application at: Apple iTunes, Blackberry App World and Google Play. All facilities which are available in web check in are also available in mobile check in. Only 4 people can check in using mobile at one time (in one session). This facility is available for passengers flying on Air Canada and Air Canada Express.
The timings of opening and closing of mobile check in are same as that of web check in.
Kiosks at the airports can also be used for checking in so that there is no need for standing in long queues at the check in counters. Self service kiosk check in can begin 12 hours prior to scheduled departure of flights and closes 45 and 60 minutes before scheduled flight for the flights within Canada and to other destinations respectively.
It shall be remembered that the check in at Toronto airport will close 20 minutes before scheduled departure for flights within Canada, and not 45 minutes. This is an exception to the general rule.
If you are carrying checked in luggage and it has to be dropped of at the Bag drop counter at least 4 hours and 3 hours prior to scheduled departure of flights from Canada/US and other locations respectively.
Travellers with Check-in Baggage
Travellers would need to drop-off their baggage at drop-off counters at least 45 minutes before departure time of flights within Canada or 60 minutes before departure between Canada and other countries.
Boarding gate closure times:
For flights within Canada and to/from US, boarding gate closes 20 minutes before scheduled departure. For other international flights including Mexico and Caribbean, closure time is 30 minutes. For Caracas in Venezuela and Tel-Aviv in Israel, the closure time is 60 minutes before departure.