Re: Getting to the W. P. & Y.

Driving the Alcan is always an adventure. If uncluttered wilderness is your thing, you'll see more on the Alcan than almost anywhere else in north America. It is however a very long drive on a two lane blacktop road, but if you enjoy that and camping along the way it can be the adventure of a lifetime. Mosquitoes can be a problem for the unprepared, but easy to avoid if you don't wear cosmetics and fragrances or eat sugary junk food or bananas. Mosquito repellents don't 'repel' bugs but rather mask the sweet fragrances and human odor of warm moist CO2 that attracts them. Any bug dope strong enough to be effective [>75%DEET] is not safe for human skin. Get the strongest bug dope available and apply it to your clothing [hat brim, shirt collar] and never to your skin. I live here and I'm never bothered by mosquitoes.
Sailing the Inside Passage on the Alaska Marine Highway is also the adventure of a lifetime and many folks do both by driving up the Alcan and taking the ferry back south.
If your main interest is railroads then a cost effective option is driving up through BC and visiting the railway museums then leaving the vehicle and riding the ferry north to Skagway. You'll still see lots of wilderness and do a lot less driving.
May, June and July are the best times to visit the north. The days are very long and the weather generally favorable. i.e.It does not snow too often. From a Phoenix perspective it will seem like winter to you most of the time while us natives will be running around in shorts and tee shirts or less.
Come north - ride the White Pass -- you'll never forget the experience.