We'll be cruising Alaska next May on the Infinity from SFO, the final disembarkation port will be Vancouver. The night before, we shall be in Victoria. We would prefer getting off in Victoria, rather than backtracking back the next day. Is it possible to disembark one day early? We are Canadians and would still have to do a customs declaration upon our return to Canada. Thanks!

I have seen people do this. But you should check with your cruise line to be sure. There should be something yo need to fill out to do this.

Early disembarkation is possible in general, but you need to get permission from cruise line beforehand (rather than just disembark on your own).
We have done that twice - one early disembarkation, one late embarkation due to schedule conflict. Both were cleared ahead of time, different cruise lines.
Also, I suspect you already know, they will not issue any credit for "missed" days on cruise.

Regent used to issue credit for missed days or pro-rated rates, it was 3 years ago when they still were called Radisson.

sorry we can't help, but we will wave good-bye to you May 21, 2009! Are you on cruse critic?