Domestic is 30 min. prior but as of 10 April moves to 45 min. prior:

http://www.aircanada.com/en/news/trav_adv/130322.html

Effective April 10, 2013, check-in and baggage acceptance for flights within Canada will close 45 minutes prior to departure – with the exception of flights leaving from Toronto’s city airport (YTZ), where check-in and bag drop-off will remain available until 20 minutes before departure.