I see on the Copa site that *G (United 1k) gets free seat selection. If I may piggyback the OP’s question, does the benefit extend to companions on the same PNR?

Edit: I called the Miami Copa office and they denied that my wife’s *G (1k) status includes free seat selection, even for her. We’re booked in Economy Classic with a T fare. I’m surprised that this would be the case…