Originally Posted by Adam Smith

According to the thread on this FP, it requires availability in V fare class.

When searching YUL-YKA on that date, V class is at 0 on all of the flights, so the FP is not bookable.

YUL-YVR and YVR-YKA each have some flights that have V space, which is why you're seeing them bookable individually.

Unfortunately you've run in to what's called "married segment" logic here, where the airline sets availability based on the origin and destination, regardless of what availability the individual segments have in various fare classes.

I don't think you can get around this by calling in, although someone may correct me on that.