My guess would be possibly Boxer/Lab. I had a Boxer that was the same fawn color. In the third picture with his stance, he looked to be built a lot like a Boxer, but that picture also reminds me of a Rhodesian Ridgeback. For the most part, shelters have to guess at what the mixes are. I'm getting ready to adopt a Beagle mix puppy from a shelter and she told me that they are just guessing at what the other half is, based on puppies from the past. Whatever your dog is, he's adorable!
I would say dauchsie mix too. There is the larger dauchsunds. You know in our rescue we had a purebred Siberian huskey give birth. Well they grew, and turns out daddy had to be a corgi. Shorty hooked up with big girl. LOL Perhaps some sort of retriever is in the mix, Maybe a nova scotia duck trolling retriever.
Whoever said you can't buy happiness, must have never owned a dog!!!!!!!!!!!