I think your plan is doable, but having driven from Mississippi to Alaska three of the past five years, and spending up to ten weeks on the road, there is no way I would attempt what you describe. You will be driving *all the time* because it is going to take many more hours travel time than you are estimating. There are so many unanticipated things that you will encounter and you simply will not be able to drive the speeds and average the miles per day that you have been lead to believe. Since you have only 40 to 45 days, I would suggest that you take your time and enjoy Canada or fly to Alaska and rent an RV.
We really did enjoy BC and YT and if you limit yourself to those areas, you will be rewarded with unlimited opportunities. If you fly to Alaska and rent, likewise, you will have the time to see much of what Alaska has to offer.
If you just want an overview of Alaska and Canada, with the intention of returning in the future for longer times, what you plan would be OK.