Smaller J cabins on certain routes is making things harder from time to time..... YUL-PEK First Class on Air China was 2000$ RT less costly than J class on AC YUL-YYZ-PEK RT this week.

There is a procedure in place for TAs to request extra seats to complete a party or fare match other carriers on high yield product. As Dorian points out some airlines give waivers still for certain fares (AC being a lot less liberal than LH in this regard)