Went through the entire thread but couldn't find the details I need.

Booked an AY ticket with the YYC to LHR segment on BA metal. Will be flying with a 2 year old child in J. Read on BA that advance seat selection will "start from" $93 for long haul international flights (still shocked at the amount they are charging). Does the same fee apply when ticket is marketed and sold by AY (benefits listed under business saver type ticket actually stated seat selection to be free)? I need to call BA for the seat assignment?

No status with both currently but I might accumulate enough points for AY Silver before this BA operated segment. Will that help in any way?