US Flights
I know it's not empirical, but just before AA pulled their proposed flights, I had a look at making a booking NCL -YYC. The transatlantic sector showed that I would have had the aircraft entirely to myself and the crew. That's hardly a good indicator that the flights were selling well !
More empirically, for all those comparing a possible Transatlantic with Dubai, don't forget the very high importance attached to freight revenues on the Dubai route. Is there any proven evidence to show that there is a similar demand for TA ex NCL ?