I have a harder time getting Jackson to walk in the hot weather

In the cold, he will go for miles. In the heat, not so much. He can't stand walks if it's above 80-85, lol.
But whenever weather is just not good walking weather- we try to take a trip to Petsmart, or another pet store, etc, so at least he gets some interaction and a bit of exercise. We also find games to play inside (fetch, hide n seek, etc).
But otherwise, I would just encourage walking and make it a positive thing. When it's hot (but not sooo hot, like I know he won't overheat)- I just bring water and keep him going, although we don't go as long. I've always liked to encourage him in general to try new things, be confident, etc... if there's a big tree trunk fallen down, I encourage him to jump on it, if there's something in our way, I get him to jump OVER it, etc, etc, I love giving him new experiences and gaining more confidence and I think it's the same sort of thing in weather they dislike. Just keep encouraging and don't give up and carry them because that's what they want! Dress warmly and on your way you go