One world sapphire and emerald would get free seat selection.

Is the flight number on your booking AA*** or AY***?

If AY and you do not have one world sapphire or emersld then yes, on AY or on BA you will probably have to pay for seat selection. Some of the more expensive fare buckets may include seat selection.

On AY, all cabins, flex ticket bucket tickets give free seat selection, others do not.

If you scroll down and select seating it says which ticket types include seat selection and which do not

https://www.finnair.com/pl-en/finnair-ticket-types

Cathay, which cabin are you in?

Economy seating policy here :

https://www.cathaypacific.com/cx/en_SG/manage-booking/travel-extras/reserve-your-seat.html

Business Class and First here:

https:/www.cathaypacific.com/cx/en_MV/faqs/manage-your-booking/seat-reservations/am-i-eligible-to-reserve-my-seat-in-advance.html