We did Ensenada MX to Hawaii on the Crown Princess one January. The trick is, like Tom wrote, it depends on your weather. We had rough weather, stormy the first couple of days and our ship was smaller and older than yours. It rocked and rolled visibly for 3 days. Some of us did get seasick, but it only lasted the first day til they got their sea legs. If you take otc or prescription meds they generally work well (check with your doctor, to make sure they are safe for you). Ginger does too, get it in capsules. If not, go to the medical center and get a shot. Most people reported they sleep for 12 hours then feel great.
Really, it was worth it. The feeling of being truly in the middle of nowhere is incredible, and the deep ocean is indescribably beautiful. We saw whales, dolphins frolicking, and flying fish jumping out of white capped deep blue water. Big puffy clouds, and water, 360 degrees around, like we were the only humans in existance. It was sooo relaxing, by the time we got to Hawaii we were ready to explore. And what a great way to see the islands---a bit of each.
One disclaimer, I was in my mid 30's on this cruise and the average age on Hawaii trips is old-very old (about 80, honest). The music was all 1930's and 40's stuff and the comedians told geriatric jokes. So if you are young and entertainment is important to you, go to Mexico or the Carribean instead
Have a great cruise!!!