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Google revealed Cheapair.com articles about how far in advance to book a flight to get a good deal on average (47 days for US domestic flights, 147 days for international flights), but are there any better articles specific to Canada?
I read this website, but its assertion below appears based only on personal experience:
If I had to pick a "good" time to buy domestic fares within Canada, I'd probably go with about a season ahead (for example, fall sales near the end of summer, or winter sales near the end of fall). Somewhere in the range of eight weeks before departure. It's around this time that it's most common for Air Canada or Westjet to get a little nervous about filling empty seats and perhaps offer a genuine sale. Don't expect miracles though; if you see a "sale" about a six to eight weeks before your departure dates, that's likely the best you'll do. I wouldn't hold out for much longer, because...