Kevin - I have lived in Alaska 28 years and driven the Alaska Highway a dozen times at all times of year. I could write volumes about the adventures of driving in the North country but I'll limit this to just a few recommendations based on your flying into Anchorage and renting a car to take south to Seattle.
If you drive fairly long days from say 9am - 8pm,it will take you about 4 days. Of course that doesn't give you much time to stop, but trust me when I say that just the sheer beauty and magnificence of it all will blow you away even from behind the steering wheel.