Long time and very regular, follower - first time poster. Appropriate thread for me, as I fly to and from Moscow at least every 4-6 weeks.
And this has always annoyed me somewhat. I can book YYZ to Moscow (say through FRA or MUC) on the Lufthansa website, flying the AC operated flight on the TATL, then connecting to LH into Moscow. But I cannot book that same itinerary on AC.com.
I realize it is because the FRA (or MUC) to Moscow flight is not a codeshare so AC cannot ticket it. Still, I was told once by AC that they have an agreement with LH that will allow them to ticket this kind of itinerary and offer it on AC.com.
A little AC trivia for fans of this route: AC Flight 876 (today YYZ to FRA) was originally AC's flight number to Moscow (SVO), flown by AC from 1966 to 1977.