Wow, are you ever lucky! That cruise sounds amazing. I don't have any first-hand experience in this kind of holiday, but last summer my parents went on cruise through Newfoundland and Labrador, which I imagine would be similar in weather? They had such a good time that next month they're going on another one with the same company, this time through the Northwest Passage. (I am so jealous of them- I have been obsessed with the NP since I was little.)
From what they told me about their experiences, and from my own boating past, I definitely agree with Angie- bring warmer clothing than you think necessary! No matter what the temperature on land, it will be cooler on the water, and you'll have the spray and wind to deal with, too.
One thing you must have is a lightweight, wind- and water-resistant jacket. Similar to the first and last ones that sarbear posted. It might be gear and not that fashionable, but you won't regret it.
On the ship, I'd stick to jeans and layers. A skirt or two for when you're on land makes sense, too. I'd also recommend camis for extra warmth, and a lightweight wool sweater or two.