I sailed the Queen Mary II, and as Lisa stated, on the formal nights a good many men wore a tuxedo. However, the men in suits fit right in as well. On the semi-formal nights, many men were in sports jacket and slacks, with others in suits.
Cunard does tend to be more formal than other lines. If there is a theme for later on a formal evening, such as a Black and White Ball, most passengers dressed in accordance with the theme. On my cruise, there was a Masquerade Ball and many passengers had brought masks from home. I didn't, and they gave out fancy masks to anyone who wanted one.
I'm sure you'll enjoy your QV cruise.