You will upgraded on nearly every Copa flight - I have only missed 3 CPUs, and in 2 of those J was already full by the time I had booked my ticket. You will get an upgrade as silver most of the time, which is 25K miles or one of the top CCs from BAC or Banco General
UA only serves IAH and EWR from PTY. Also there is no PDQ needed for Copa, however that will be the same with your United account should you also move it to Panama