Several dog breeds are quite useful as draft animals. St Bernards and Newfoundlands both can outpull a Husky. Saints regularly pull 10-12 times their own weight in pulling contests. This is around a ton of concrete blocks on a sled on dirt with no wheels! What's more they love to do it. Bernese and Greater Swiss are also traditionally used as draft animals.
So, a St. Bernard is the dog to use as a draft animal. I suppose you could cut the dog's hair to compensate for summer heat. (any breed) In Illinois animal-propelled vehicles are legal without a license due to a small number of Amish types.

You'd still need a pet friendly workplace to "park" your dog by your desk. It sure wouldn't be nice if the workplace merely had a kennel as a "stable" as you work.