Best time to cross into Canada for Alaska trip

My wife and I are going to Alaska next spring/summer. We are retired and will be spending at least 2 months there, maybe longer. The first big question we have is when to go. What are the pros and cons of going in mid to late May? Are there advantages to being there in September? We want to see wildlife (bears) and enjoy some fresh salmon. My wife would really like to see the northern lights, but that’s probably not going to happen in the summer, right?

We will be driving a 24’ Sunseeker MBS with no toad. With a small MH like that, I am thinking that we won’t have problems getting into campgrounds, except for holidays and Denali.