Are you saying both ends of the Panama Canal are not at sea level? Pump water to the lake and keep it flowing.
The canal is above sea level. That’s why there are locks. The locks do not operate on pumps. There are no pumps. There is no power supply to run pumps. That’s not how a canal works.
The canal is fed by FRESH water, derived from rain and stored in the artificial Gatun Lake. Said fresh water is fed by gravity into the locks, and then into the sea (where it would have ended up without the canal). It’s a simple and elegant system. Don’t fsck it up.
And that’s what the ChiComs did: they fscked it up. The original designers knew how much rainfall to expect in Panama, and designed a canal to use a bit less water than that. The ChiComs doubled the canal’s carrying capacity without doubling its water supply. And now the canal is in trouble. Duh.
Pumping huge amounts of saltwater into a freshwater system, aside from consuming astronomical amounts of electrical power, will also screw up the system. The plant and animal life in and around the canal is freshwater, not saltwater, life.
Seriously: gravity fed canal locks are an elegant engineering marvel. If such things interest you at all, your time would be well spent learning a bit about how they work.