If it’s polished bronze, you’re in for a struggle, raw bronze just
loves to oxidize. There’s a reason you don’t often see sculpture
without a patina. : ) Brass would be better if you’re trying for a
polished look that lasts.
The best finish is Carnuba wax, you can buy it at a decent hardware
store or even some auto parts places, try to get 100% Carnuba. Warm
the piece up however is convenient and wax it up. When cool, wipe
off the excess. It won’t last forever but it’s easy to reapply and
doesn’t remove any metal or change the underlying finish with
Don’t try to coat it with any type of sealer, polyurethane, varnish
etc. The bronze will still tarnish underneath and/or the coating
will get scratched and look lousy. You will then have to strip it
and refinish the metal before resealing.
The gold plating should be fine, it’s gold after all and won’t