It's funny you mention Cunard. I had done a ton of research many years ago about sailing with Cunard from NYC to, I believe, Southampton UK, with my large dog, en route to Europe for graduate school. I didn't end up going that route, because Cunard had a very small number of dog kennels available on their vessle (I recall only a dozen or so) and so they were typically booked out 1+ year in advance And this was well before COVID.

And also, the idea of sitting on a boat for two weeks eating buffet food with a bunch of retirees sounds like just about the most tedious thing imaginable.

Furthermore, the kennels Cunard did have available on their select pet-friendly vessles were not too large, so if your dog was over a certain size, and I believe my average-sized 100-pound Ridgeback was, you would have to book two adjacent kennels or something weird like that, which considering the limited available of the kennels, basically halved the likelihood / doubled the timeline of your finding a booking.

The pricing was not too bad, compared to the alternative of finding a flight, and acquiring a crate. But the logistics and timeline did not work for me.