Initially every cat hates the harness and leash. We used positive reinforcement to get the cats adjusted to wearing the harness- like putting one on them just before giving them their favorite meal and then leaving the harness on them around the house for a while.
Once they would wear it without fuss, we added the leashes and took them out for a "carry" around the yard. After a couple of those, they wanted to get down and sniff. Over time they began to walk along while wearing the leash and harness. It's still hard to steer them, but eventually we get where we need to go.
Our big guy now starts to purr when he sees his leash because it means he gets to go outside with us. You can teach cats to tolerate, if not even enjoy, leash time.
p.s. never hook a leash to a cat's collar - either the collar will open (safety collar) or you'll strangle the cat as he does advanced yoga trying to get it off of himself