Do cargo ships leaving from Le Havre go across the Atlantic to the United States? I mean the really huge ones - it needs to be big enough for the characters to sneak on relatively unnoticed. If not, would a different port (like Saint-Nazaire) be better?
I wikied 'Le Havre', 'Saint-Nazaire' and 'Sea transport', but nothing was really specific enough. Googling 'France to America shipping' and variations thereof was similarly unhelpful.
Edit: OK, thanks - I've got what I wanted, though I'm going to have to think a bit harder about the immigration side of things. Nothing's set in stone yet.