Crossing the North Pacific at any time is somewhat iffy. It can be smooth as glass with bright sun, or storm tossed. Although cyclones (hurricanes) usually do not go that far north, it can happen.
For your repo cruse on the Millennium(?), I'd expect air temperature to be in the 50's. Sea temperatures should be in the upper 40's. I would expect allot of wind which will make it feel colder. And, if you run into a storm, I'd expect rough seas. The Captain will do all he can to avoid the storm. Your average wave height would be about 12 feet. But frankly, that is a guess. And, after thinking about that for a bit, I'd raise that total to 12 to 15 on average. Not a problem for the Millennium.
Hopefully, some other C@ who has made that crossing will chime in.