Leash-training a young Bulldogge puppy?

The leash needs to mean something fun to the dog.
My dog’s like the leash because it means going for a ride in the car, which they love.
So the trick is to follow the putting on of the leash with something the dog really likes before (or perhaps after) going on the walk.

If the dog responds strongly to food rewards, you could try starting with teaching the heel command. Since the dog is already sitting, you stand on the dog’s right with his front legs parallel to your legs. The leash should be in your right hand, crossing over your legs. Take a treat in either hand, fold up the excess leash in your hand so it doesn’t get tangled, then bend down very low, put the treat right in front of the dog’s nose, then say “dog’s name”, heel and start walking with your left foot, quickly. Stay bent low and slowly move the treat in front of your left leg to keep the dog close. Hopefully he will follow the treat and stay with you. This will probably have to be done for pretty short distances at first, and repeated a lot before you can dispense with the treat and walk upright. But won’t you be the envy of the other dog walkers if it works.

If he suddenly act so differently,then something must trigger this action. What happen to him a day before he’s changing his behavior?(dog can usually doing this for protest with changing environment,lifestyle,food,etc). Try to find and solve the problem first(provided laziness is not his nature).

@Doctor_D
It’s not a different action. When he’s off-leash, he’ll walk with me. When he’s on-leash, he won’t.

Is the carrot-on-a-stick the best option?

I don’t know about any specific option being the best, but you’ve got to find some way of making him want to walk on the leash, and some kind of reward for doing so is usually the best approach. You could combine my suggestion with @Grisson.‘s Say your dog likes to go for a ride in the car. Never take him in the car without taking him to the car with the leash on. Use the heel command to get him to the car with the leash, then let him enjoy his ride, maybe take him to the park if he likes that. A few tries with that and he’s likely to walk on the leash. You should also give him lots of praise once he is walking on the leash.

One other approach, if he is well potty trained, is not to take him outside without the leash (if you take him out without it now). When he has to go, he’ll move leash or not. Then you can praise and reward him for walking on the leash.

@Seek Kolinahr Yes,but after he get the bait it’s all over(he will lazy again). By doing so you only make him spoiler,and he only wants to move if you treat him with his favorite bait(more treat also make him fatter). I believe an animal behaviorist or veterinarian will inspect and solve this problem better,or if you wants other alternative way.