From my experience, I think this matchup is slightly in fox's favor. I generally beat G&W's including going 4-0 against NoJ's G&W tonight.
I just do sh single lasers over and over, wait for him to do something, and then react.
You should keep the lasers coming but only laser right before you get to the ground. That way you can stay mobile and hopping around, you get some damage in, and he can't punish your laser by jumping in with something because you'll see it coming before you shoot the laser.
From a neutral standpoint, if you're jumping around shooting lasers, his main options are jump with a bair, nair, walk or run up and shield, or walk and do a tilt.
With single lasers, if you see him try to bair or nair, you should just not laser, and instead jump and punish with a dair. Careful not to land on the nair or you'll get hit. Pay close attention to your fall speed and make sure to change things up accordingly to get in there when he has lag.
Watch his patterns as far as approaching on the ground. Single laser and then grab or upsmash is good. Grabbing's really good. But don't be too hasty on your approaches if you can't see his pattern. You can always just jump over him and get away shooting more lasers. And approaching when he does this is kind of a rock paper scissors thing, whereas punishing their attacks is not, so doing has a slight more risk of getting hit.
When G&W is in the air, try to keep them there. Keep somewhat close to them and try to punish whatever they do. If they key after getting hit, you can jump then wait a sec, then double jump to fair. If they key into the ground, just watch for it and grab them on landing, dair, or upsmash them. If they turtle or nair, jump over it and dair them. If they airdodge, just get to the ground before them and punish it with a grab, dair, or upsmash.
Don't dair them when they can just shield it. (meaning use it only to punish attacks or airdodges or spotdodges or rolls or other punishable stuff.)
Also, G&W dtilt is a *****. Powershield that **** and make him stop doing it.
edit: And don't get hit by an utilt at low percent cause he'll combo you to over 70%. It's stupid.