jloving....Are You departing from an East Coast or a West coast Port? From an East Coast Port it is likely You will cruise around Cape Horn requiring the use of the Drake Passage which is usually rough or a Magellan Passgage which can be difficult!! I have not seen too many TransPacific Cruises using the Panama Canal but they do take place!
Holland America does offer some very nice TransPacific Cruises using West Coast Ports...You might also give them some worthy consideration!!
If it gets rough there are SeaBands, Ear Patches, Green Apples and Ginger Pills....On a TransPacific multi day cruise You will certainly gain Your Sea Legs!!!