The one time we did BA to WS on a single ticket, the WS legs booked into the cheapest economy buckets and we got nothing in terms of benefits except the CW baggage allowance on all legs (but there again wasn’t expecting anything else either). I paid for seat selection but it was silly cheap compared to BA. Something like $10 each.

The kids were young enough for us to get pre-boarding anyway, so that was irrelevant.

I did notice that that other airlines that connect to WS in Canada like KLM do book into the extra legroom seats when you book longhaul J.