The key to cruising in Alaska, is to dress in layers ad adjust as the day goes...When you are out on deck, you will need a warm jacket and it will also depend on what excursions you take. We did a whale watching excursion in Victoria and while it was reasonably warm, once out on that open water late in the day, it was very cold. They luckly had some warm parka's for everyone...
Be sure to pack some rain gear, most likely you will see some along the way...
What are your ports and are you cruising from Seattle, Vancouver?