Hi, your baby is incredibly cute! Harnesses are considered safer, as they don’t press on neck and dog cannot get out of it. My bulldog was ok with harness, but I noticed that his fur in his armpits looked shaved, and the problem persisted no matter how loose I made it. So I stopped using it and we use a collar, for 2 years already. But I must say my Tank is extremely obedient and he is not a big puller. Even if he wiggles out of collar when sniffing other doggie, he will come to me to put it back.
If you still want to get your dog used to harness, first of all you mustn’t pull him like on photo. Bulldogs are stubborn, get offence easily and have good memory, so if he will make association between harness and pulling, he will hate it more and more. And he will make walks difficult for you, as he has, you know, four legs and being more stable and closer to the ground he can pull better than you
To make harness a positive experience for him, put harness on just before you give him food. So he will associate it with good things. Then leave it on for the whole day on. And never pull him. I know, bulldogs sometimes are very irritating with their ideas that they want to take a rest when you need to run home in time to get dressed for work etc...but, it’s better to pick him up and carry for a while than to pull. They are very intelligent and manipulative dogs, and unfortunately for anything you want them to do or move somewhere you have to 1) bribe them with treats 2) give a lot of positive feedback 3) if cooperation isn’t achieved just give up or nonviolently move Bulldog from place to place using your hands.