Are they really "properly" cancelled? I have had occasions where agent told me the booking was "cancelled" but it was actually not, only the ticket was cancelled but not the reservation.
Those reservations linger in "my bookings" both on AC web and AC app. And if I make a new booking with the same itinerary, the new booking will be marked as "duplicated". I have had cleared EUP cancelled without notification (the reservation is gone silently, the same behaivor as a duplicated booking). I also notice the spaces from those "cancelled" bookings don't go back to the inventory.

I have to call AirCanada (cash tix) and Aeroplan (award tix) to ask the agent to properly cancel those reservations. You might need to HUCA to reach someone who actually knows what's going on, and they have referred the operation they performed as a "profile update" (I have no idea what does it mean). After "properly" cancel those reservation, the bookings will immediately vanish from "my booking".