Basil wrote:
Day 1 - Seattle (Depart)
Day 2 - Fun Day at Sea
Day 3 - Cruise Tracy Arm Fjord (We plan on doing an excursion up one of the Fjords)
Day 4 - Skagway - Probably do one of the scenic hikes
Day 5 - Juneau - Whale watching excursion
Day 6 - Not sure yet what we want to do
Day 7 - Victoria BC - Again, have not decided
Day 8 - Return to Seattle.
First...do you know for sure that your cruise will be cancelled? Even though these cruises are marketed as 8 day cruises, they are really only seven days in length. Depending on what the rule specifically says and requires (a full day for cleaning and sanitizing, for instance), your cruise might still fit within the rules if Canada opens its ports to passenger ships.
Second...have you been on a cruise before? If so, I suggest that you rely on your experience more than our biased attempts at telling you what to do. If not, I suggest that you plan to spend a lot of time just enjoying your first cruise.
Third...it is very hard to provide suggestions without knowing more about how you work and what capabilities the equipment you have provides. I see that you have significant engineering experience and that you have been pretty deeply involved in photography for a long time, so I'll try to provide some general hints based on my experience that may be of some help.
My wife and I did a cruise from Seattle to Alaska and back a few years ago to commemorate our anniversary. We enjoyed it greatly. It was a "hosted" cruise, with activities provided by folks with whom we were familiar, but we still had plenty of time to do all the normal "cruise stuff." I was not as oriented to photography at that time, but did come back with lots pf photographs.
I did not have a long lens, but I did not miss it at all. The long "days at sea" are really long days at sea. You will be far out from the coast and no land will be in sight. Depending on the season, there may be a whale or two spouting in the distance occasionally, but other sea life can be hard to spot, other than a few dolphins swimming right against the ship. We did not see wildlife while on the detour through Glacier Bay.
Skagway is a small town. It was a key part of the gold rush. The hike might net you some wildlife, but I'd check to see. Ketchikan is a lumber town. The lumberjack show is at a fairly small outdoor arena and would provide some good opportunities at near to medium distances. Juneau is the location of the Mendenhall Glacier, which is becoming disappointingly less impressive each year as it recedes. By the way...there is a likelihood that you will have to "tender" into town from Ketchikan or Skagway (can't remember which). If so, the ride is nice, but crowded. You don't want to be messing with a carload of equipment for that stop.
Whale watching is a nice activity but often disappointing. We saw no whales, but a number of dolphins. Federal law prohibits approaching within 100 yards of humpback whales, and state laws prohibit approaching within 200 yards of Orcas. Whales can approach the boat, of course, and when that happens, the captain is required to idle the engines and shift to neutral until they have withdrawn. The wind doesn't have to freshen very much before the ride on the whale watching boats gets quite rough. That is usually not a big problem, but the salt water spray can be. There are sheltered areas on the boats, but they are not suitable for photography due to sharply reduced viewing angle and Plexiglas wind screens.
Victoria is a treasure. It is very clear when you are there that you are "somewhere else." Architecture is interesting, as are museums. Streets are not overly wide, so you are going to be shooting from space that is somewhat confined. Butchart Gardens are worth a visit, but the time may be too compressed to make it worthwhile. They are worth at least a half day (or more). And the Princess Hotel is definitely worth stopping in. One caution: The Canadian people are beautiful and friendly, but my experience is that they have little interest in US currency. Plan to pay with Canadian currency or with your credit card while there.
I second the suggestion to take binoculars. I disagree that 10x binocular are a good choice onboard the ship. Too much magnification to manage against the motion of the ship. Take a pair of 7x50 in some of the space opened up by the photographic equipment you left at home and enjoy the wide field of view. (You can stop in at Captain's in Seattle if you don't have a suitable pair to take from home.)
If I were going on a cruise to Alaska now, my plan would be to take my D850 and a 24-120mm f/4 lens, along with a small flash (like an SB-400) to provide a little bit of fill if needed. Any shots that needed a longer lens would be framed with the intent of cropping later, maybe to the equivalent of 250mm or so. If I miss some wildlife opportunities, I just miss them. If I see something wider, I'll make a panorama. Monopod? Maybe. Tripod? No. Late spring and summer are not aurora season, and night sky photographs are not going to be possible anyway.