You may not be able to figure out exactly what your flights are going to be this far out, but there will be a LOT of options. Let's say you're coming out of Amsterdam, for example - Delta has a big operation there, and while CVG is by no means a Delta hub anymore, it still has a sizeable operation. So, in that case, you're likely to have a ton of options from Amsterdam to CVG via Detroit, or Minneapolis, or Atlanta, or New York. In each of those, you should have multiple options which will allow you to build as long or as short of a layover as you're comfortable with, especially Detroit/Minneapolis/Atlanta.
If you can't book flights now, and you're not willing to book the cruise with unknown flights, I'm not sure what else we can advise on. You'll have to either wait for flights to be released in about a month, or risk it. Just be aware that booking flights right when they come out usually results in schedule changes over the subsequent 330 days.