It seems to me Cunard is the last bastion of pure formality, especially a transatlantic crossing on QM2. I have not seen that many tuxes on one ship since my days working for Royal Viking Lines back in 1982/83.
On RVL everyone wore a tux. Some men actually had custom made tuxes of powder blue or purple with paisly cummerbunds, etc. It was quite the show.
On Cunard you should not bring a white tux- that is what the dance hosts wear.
Does Seabourn still have gentlemen hosts? I heard they ended that program.