How do you get cheap international flights?

Well accually
1.NEVER USE AIR CANADA
2.Try the big good airlines because they often have seat sales.Also the small discount airlines like westjet are always good bets.
3. Use airline consolidatos services. Consolidators work through contracts with major carriers to manage blocks of airline seat inventory at reduced prices which they then sell. Fares through consolidators will be lower than published rates available from the airlines themselves. For example http://www.travelpapa.com/