What are the "musts" to see/do in Panama? This trip will be adults only.
I want to sail they at least part of the canal and go they locks. What "cruise" company is best?
Where do I go to watch the sun rise over the Atlantic and set on the Pacific?
Best bars?

The majority of the cruise lines are partial transits. Full transits take longer. I know Princess offers a full transit with an additional day in Fuerte Amador. Windstar is another one. My in-laws did the Princess one and thought it was amazing. You start in California and end in Florida (or vice-versa).

Contacto bars are are always a fun time.

Casco Viejo in the city for the bar scene

Make a trip to Taboga island from the city, you can take a ferry to it (multiple departures) or book a catamaran booze cruise on Viator for ~$90 a person - It has a few beaches and a nice area to stroll around for a few hours -

https://www.viator.com/searchResults/all?text=taboga%20island&destId=749

https://tabogaexpress.com/

If you are adventurous, book a trip to San Blas islands on the northeastern coast (also on Viator), its a full day trip ~$150 person
https://www.viator.com/Panama-attractions/San-Blas-Islands/d749-a19712