If the cats are comfortable with dogs than this will be very easy for you
Even easier since the dog is a puppy and a lab who are usually very good with cats. Put the dog in a crate and let the cats sniff, hiss swat at what ever until they calm down, give the dog treats while he is in the crate. Once the cats seem calm you can bring the dog out on a leash but keep him a distance away from the cats, give the dog treats and praise for calm behavior. If he snaps lunges or is just overly excited do not scold just hold the leash and ignore him. You should not scold because the cats should never be associated with negative things. If the dog is not acting aggressive than let the cats walk right over and sniff him. If the cats are comfortable let the dog sniff them. Do this for a few days or weeks until they all seem very comfortable and then let him off leash around them while you supervise. Do not let them together unsupervised for a long time until you are 100% sure they will be completely fine. You can also let them meet through a baby gate since nobody can bite or scratch through those but can still sniff. I would not delay until the dog is bigger, you'd rather a dog that grew up with cats than one who meets them in his uncontrollable teenage years
Just as I said don't leave them unsupervised and give lots of treats for calm behavior! Also make sure the cats have a place they can get away from the dog. If you baby gate a room that has their litter box (some dogs like cat poo too) and their food (dogs like that even more than the poo) that would be good since they can get over the gate and the dog can't (yet). Also a cat tree would be nice or a high shelf so they can sleep in peace. Good Luck!
edit: I just re-read your post. 6 weeks is very young for a puppy to leave his mom and litter mates, where did you get him? Most breeders wait until 8 weeks at the earliest and some prefer 10-12 weeks. You need to make sure you super socialize this puppy with other dogs and make sure he learns how to play nicely which he would normally learn from mom and siblings.