I wish that anyone around the world could dog sled at their own location, but unfortunately that is not the case. The best dog sledding environments are the ones that have tons of white fluffy snow and it has to be in vast expanses of the open terrain. There are various locations with these ideal characteristics and luckily they aren't ALL in the same place, but Alaska is where you want to be if you are interested in any long races. There are other countries such as Switzerland, and even out west in the States, but those places would still be hard if you wanted to go long distance.
Northern Alaska is great spot for those are seeking to take long adventures because the terrain is always covered in snow for most of the year and it has beautiful scenery. If you do plan a trip there, be sure not to get off the beaten path because you could get yourself, and your team in trouble if it is a new location you are unfamiliar with.When planning a journey, make sure you plan the route ahead of time and make sure you are only a few miles away from help in case of an emergency. This is not possible in many of the less populated places up north, but still talk to local guides to see which routes are the best and safest.