Replying to Leon's comment. The one thing that our journey underlined is that you do not require a larger tow vehicle than a Highlander for a trip to Alaska particulrly if you only have two people on board (we had 3 for part of our journrey as our son flew up to Anchorage and joined us for two weeks). The majority of the Alaska Highway is fairly level the only real exception is Summit Pass which is a less severe gradient than most Colorado climbs. The road up from Skagway to Whitehorse (a must see for any trip) is the most severe challenge that we found and this is long (8 miles) rather than steep and the Toyota took this with ease and without any indication of water temperature increase.
Frost damaged roads rather than steep climbs are the main hazard on a trip to Alaska. You can maintain 60-65mph on a lot of the Alaska Highway but you will be restricted to more like 45mph and slower on some stretches and on many other Yukon and Alaska roads due to the seasonal frost heave. The worst stretch is north of Haines Junction in particular the 200 miles south of the Alaska border. The object of this journey anyway is not speed but the enjoyment of the wild scenery and chance of viewing wildlife i.e moose, forest buffalo, bear, wolves etc.
My recommendation, go for it and have the journey of a life time! I would strongly suggest that you take the route from Calgary to Banff and up the Icefields Highway To Jasper and then on to Dawson Creek which is the beginning of the Alaska Highway. This is a much more enjoyable route than going via Edmonton. The road betwen Banff and Jasper is one of the most spectacular in North America (wait for a clear day to travel on it).
Another important point, when driving on the Alaska Highway do not let your gas tank get too low and top up at every opportunity. I tried not to let the tank fall below half full as some of the distances between gas pumps can be long. Also expect to pay more for gas on the highway in British Columbia and the Yukon. We paid on average between $4.30 and $4.96 per US gallon at current exchange rates.
Good luck,
Geoff Card