Please note that most of the cruise lines stop in Ketchikan, Juneau and Skagway. Some of the smaller Holland America ship also stop at Sitka. Also due to the late afternoon departure, most of the first part of the cruise is done at night, and by daylight the ship is already out of of Queen Charlotte Strait into open water.
We've done one cruise out of Vancouver to Whittier on Princess, and 4 round trips out of Seattle and have never had really rough weather on any of them. However, the September trips have a higher occurance of rainy windy weather.

Either Holland America or Princess can handle elderly passengers quite well. Does your father have any other physical problems other than his eyesight?

Hope you find something for him. We love cruising because we only have to unpack once and meet lots of interesting people.