With this itinerary, you are FAR better off going northbound, since Inside Passage drops off significantly with weather compared to interior Alaska which can be more milder. Also you may not realize, if going southbound, is you are going to have dusk by 7pm.
I hope you know everything about what you have booked on your Princess cruisetour?? And hopefully, it is at least a 5 day add on tour. The most important point, to consider, is get into the park, with the Tundra Wilderness tour, I would never accept the Natural History tour, especially in that timeframe.