They can’t just reduce the length and do Alaska as shorter itineraries if Canada still isn’t allowing cruise ships and is requiring two weeks of quarantine (and as someone who lives in Canada I would not hold my breath on those restrictions lifting anytime soon. The CDC doesn’t make the call on cruises from Canada.
Without those restrictions going away they’d have to figure out a way to sail out of Seattle. Maybe they’ll do that but there’s a lot to work out to make that happen.
I understand Canada is a big if. I said I am confident they will find a way to do Alaska, even if they have to reduce the number of nights, unless there is something prohibiting from sailing (e.g. Canada). I still think the Wonder is going through the canal one way or another this year.