I live in Vermont. The weather here is just as mixed and harsh as Alaska.
Vermont is not as mixed and harsh as Alaska, but I think the 5D3 would most likely fill his needs just as well as the 1D4, and possibly better. It doesn't sound like he is going to be out on glaciers on a regular basis, and since he didn't mention what type of photography he is doing its kind of a guess on all of our parts.
PS- I love Vermont, and I'm not sure there is a more beautiful state to be in the fall.