Last year I went on my first (and most definitely my last) cruise. I was on a Princess ship that went from San Francisco up to BC and into Alaska. First, let me say that trying to "see" Alaska by boat makes about as much sense as going whale watching in a Jeep. You get into port after 9 AM - so as far as great light is concerned you're already dead in the water (no pun intended). Then you've got to be back on the ship by around 5 PM, so once again you're going to miss the great light because you're stuck on a boat.
Okay, so is there an upside? It really depends on what type of photography you're going after. I assume you're considering renting for capturing the landscape. If you take advantage of some of the excursions like the helicopter ride you'll have some unique photo ops and you'll get away from the main port towns which are just for shoppers and aren't very photogenic. Otherwise, I'd say the only real photo ops are when you're going through the fjords which is usually near the last day in Alaska. Having a WR camera is very helpful in many situations on/off the ship. While most people were inside, there were a few people, myself included, on deck with WR cameras (most were Pentax) taking shots.
As for lenses I think most photographers will either be very wide or in fairly close. I found myself using my widest angle lens (18mm equiv in APS-C or 28mm equiv in FF) the most and if I was switching to anything, it was usually to my strongest telephoto. So, yes, I'd strongly advise anyone who's into photography to rent a WR body and the widest possible glass too. You'll probably not bring a tripod with you for obvious reasons. Instead of a traditional tripod, I brought a GorillaPod and it worked great. It's only about 1' tall, but that's fine for resting on walls or on the ships rail.
P.S. If you're going to Butchart gardens, for my group we all thought it was a great place. There's a butterfly exhibit near there which was considered by my group to be a total waste of time. I'd encourage you to get up in the AM and watch the tugboats bringing the ship into port; I got my favorite shot of the cruise at 5:45 AM on the last day as we pulled into San Francisco.
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