If you can afford 2 weeks off for a round trip, you should really take at least a week in the country to arrive at to see it. Cruises are nice, but you don't see the culture of the places you go. Either fly back, or take more than a two weeks. I recommend fly back, the one way trip is a once in a lifetime thing, but the return trip seems like it would be repetitive (having taken several cruises, though none trans ocean)

Of course both Europe and North America are large continents with a lot more to see than you can do in a week, but few of us have the budget to be a world traveler for a few decades to see everything.