It seems to show up on basically any TPAC itin with a north american AC codeshare or segment. Search from YYZ->BKK on 6/24. You'll see lots of such segment options appear on both AC and AC Express flights. If you search for F cabin explicitly, you always get them. But even searching for Y cabin, there are a few options that appear at the bottom of the by-Price list, oddly, not the same as the ones that appear for an explicit F search.