The part about dress in the MDR depends on the cruise line.
Some enforce the no jeans , etc in the NDR at night . Others don't .
If we knew the cruise line probably could give a better answer.
The weather during the day is very changeable , rain , sun , clouds
and snow within a space of an hour . Especially on tours that take
you to higher elevations or on the glacier.
Be prepared for all types of weather.
Some years the temperature
in the Seattle/Vancouver area could 80+ degrees.
Go to the following link and search for the historical weather with the