How long before the flight should I start searching for availability NYC-YYZ? now it doesn't show anything available looking at the beginning of Aug.
(Anecdote: Last year my son got engaged around this time . Wedding in mid Aug in YUL. I panicked when there were no BA seats and booked the choson and my father on united. Over the engagement period, seats opened up in drips and drabs. I booked my married daughter and her family, and 4 couples (sisters and sisters in law). I drove with the rest of the family.)
Advice: Relax. Keep checking. Seats will open up over time.
When I book my (other) son back and forth to yeshiva in YYZ, I most often find something - even ( especially) in the last minute. But availability changes in an instant - keep checking.