Actually, Holland America doesn't have a coat/tie requirement any longer. Even with them, a pair of slacks and a collared shirt would be sufficient. On Cruise Critic (CC), I've seen posts stating some folks have even been able to attend Gala night in a nice pair of jeans. And as mentioned above, Alaska cruises tend to lean toward less formal than cruses in other locations.

Note I have a HAL cruise in Alaska coming up in 3 weeks. So I've been searching CC for this same type of information.