We did the tour after the cruise, because it was a TA fam trip and that is the way HAL arranged it for us. It worked fine.
A consideration is, that a pre cruise tour usually ends up in Anchorage and you board a SB cruise. We happen to like the NB cruise itinerary better in most cases.
Also, if you are doing as we did, a 3 day portion of a cruise followed by the tour, we prefer leaving from Vancouver or Seattle and doing the first three days that way.
Check out our trip report and pictures at Alaska Cruiestour – The Cruise
Have a GREAT cruise!