For the most part, it'll have to be a round trip unless the ship goes to or starts from Mexico (some place called Ensaneda is popular) but on large MM ships. Otherwise and also for OW, it'll usually have to be from Vancouver to avoid PVSA (Jones Act is for cargo, though pax on the MM lines might as well be cargo). Ponant ran a 9-or-so-nighter Vancouver-Honolulu 1 1/2 years ago but that doesn't seem to have any in the future schedule (ship did an Arctic transit, came down the west coast, and repo'd to either Japan or Australia.)