I'd look into a rescue dog sling like the airlift fido pro. Idk how comfy they are, I only carry mine for emergencies and have only used it to test. The stroller is more tricky, I think they do make bike trailers to hold dogs, or if you are crafty you could look into rigging one, but idk if they can handle trails. I used to take my BOB stroller on all sorts of crazy trails, but idk if you could rig it to carry a dog.
Some of us have large dogs that like to go places and see other dogs and people more than anything else but eventually time robs them of their mobility and via this way we can continue to make them happy until it's time to cross the rainbow bridge.
The company K9 Sports Sack makes a number of different carriers. They have sizes x-small to xx-large. Their sizing is based on length, not weight. I have one for my 11 year old Boston. I use it occasionally, and even with him at 27 pounds it can get heavy after a while. I'm physically strong and lift regularly but having him on my back for a while can be much, especially while crossing water. More info on sizing: https://www.k9sportsack.ca/pages/sizing
The big issue I have with these bags is getting your dog used to being carried, and also getting up with the dog on your back. 100 lbs might be challenging, especially if you're alone. If you have more questions, happy to share my experience using one of their bags.
Maybe you can modify a game cart or search for all terrain wagons.