I think they travel both down the Taku and can make their way down from Haines and Skagway. And even the ice fields are possible, but probably not likely for a cat. I knew a trapper that was flying over the ice fields one time and spotted a pack of I think 12 wolves coming from Canada. He followed them for some time, and eventually figured where they were headed. Being a very experienced trapper, he set about trying to trap them.
It wasn't long after that he collected all 12!
Also, a wolverine that was captured and collard in the area of my main trapline up there was tracked over the ice fields, then lost, (this was north of Juneau, about 40 miles). 2 years later, it was trapped by a trapper up Telegraph Creek!!!

Hand in the cookie jar, and paid for it.