I prefer Google Maps. It usually gives 3 route suggestions, with distance and time estimates. It is also easy to 'grab' a route and move it around, passing through different towns or using different highways. With a distance like FL to AK there must be dozens of alternatives that differ by by only 100 miles or so. With a month or more of travel those kinds of distance differences are minor.
Also take travel times with a big grain-of-salt. They are based on speed estimates, estimates that might based something as simple as the typical speed limit for that type of highway.
Between FL and northern Alberta/BC there are all kinds of alternatives, since most of the area is flat with lots of towns and highways. After that there are few choices - the Alaska Hwy or Cassiar to Yukon, and a couple beyond that. Get something like Mileposts to read about those highways.