Surely going to aircanada.com and look at "my bookings" and then either "all my bookings" or entering with the specific AC booking reference, then going to "see details" for a specific reservation, near the top and under a grey box with "Booking reference XXXXXX", there is, under a lighter grey background, and in a blue frame, "Lufthansa ZZZZZZ" followed by the text "We've provided additional confirmation numbers for your convenience. You can use them when contacting other airlines for seat assignment or reservation assistance with this trip. "