We have an inflatable, 2-person kayak but did not take it to Alaska. As others have said, the water in the rivers is too cold and it's too rough in the Lynn Canal, Cook Inlet, or Turnagain Arm (not even mentioning the hazard of the bore tides!). I have rafted on the Nenana River in midsummer in a dry suit, but my face and hands still froze.
As Sue's photos show, lakes are your best bet, but even lakes in northern BC are too cold for me. We might have used the kayak when we were in the Okanagan Valley in southern BC or in the US Rockies, but it wouldn't have worth carrying it for 10,000 miles just for that short time period.