In Vancouver we had arranged the cab ahead of time through Princess, but I know we could have just called once we arrived at the airport (from others who did this).
I noticed you are also going to Skagway. From the pier it is about 1 mile into town. There are shuttle buses here and about every 4th one is wheelchair accessible. Ask the shuttle operator at the pier to call and see when the next one is coming. We took the Whitehorse Pass train ride here (1/2 day). It comes right onto the pier, and one car is accessible with both a life and a wheelchair accessible bathroom. No tie-downs, but space for wheelchairs (and it never goes very fast). We booked this through Princess as the ships often take all their tickets.