I would love to do a cruise that stops at every major US port from Boston to Seattle.
Actually, it would be no problem at all -- so long as you include a stop at a "distant foreign port" on the itinerary. Since you have to get from the Atlantic to the Pacific, a stop at a "distant foreign port" would be a very minor detour.
>> If you go through the Panama Canal, just stop at Aruba, Bonaire, Curacao, or Cartagena en route.
>> If you go around Cape Horn, just stop anywhere in South America -- Rio de Janiero, for example.
>> If you go the long way, any port of call in Europe, Asia, Africa, or any foreign Pacific island would meet the requirement.
It could be done!