Perhaps
has what it takes? Any fruit between Cherry and Melon are going to be blocked by the dog's Gunmen, Cans, and Clays. Said blocked Fruit will also be up for grabs once it collides with your arsenal, especially Gunmen, due to its quick & low endlag. Do note that you'll have to dash or air attack it to pick it up, otherwise said blocked Fruit will still hit you. However, as soon as Pac-Man reaches Galaxian Ship (?), consider your projectile shields ripe for piercing. Hydrants knocked your way will also pierce your entire arsenal. The water from Hydrants will simply pass through your arsenal without messing with any of them.
If you DO catch a Fruit, you can try to hold on to it as long as you can to deny him the ability to throw any more Fruits. Of course, by doing so, you'll also deny yourself the ability to use any A button attacks (including Smashes!) and grabs as well. As the canine, your overall mobility is pretty good (you can even crawl & wall-jump!), and you'll still get to chuck Cans, Gunmen, and especially Clays. These will become your main sources of damage dealing if you decide to hold on the Fruit, because without his Fruit, he'll likely try to approach you, especially once he sends the Hydrant flying your way. Hitting him out of Power Pellet before he eats it by hitting the Pellet itself will allow you a chance to heal yourself a bit from the Pellet he drops. If you're still holding on to a Fruit when you try to go pick up the Pellet, you may have to throw it away in order to heal yourself with the Pellet. If there's a way to pick up the Pellet without having to throw away the Fruit first, please let me know. Trampoline will beat your Can, which is one way he'll defend himself against your edgeguards. A DH without access to A moves & grabs (due to holding on to Fruit) will have to play a ranged game like Marth, and possibly even counter-camp.
As for challenging this fighting style as
, much like every other MU, the high ground, FAir --> Neutral A string/DTIlt/UTilt x? --> UAir x?, and Side B Jump Cancels (including Side B --> JC [--> UAir at 75-ish%] --> Up B --> A [Hammer] at around 100% for the KO) will be key. In the middle of Side B when Pac-Man's throwing Fruit or sticking out Power Pellet or FSmash? Jump Cancel over it and either try to aerial the Fruit into your hands and/or approach him from there.
It is true that the Hydrant is an effective defense against Mechakoopas. However, Mechakoopas and uncharged Cannonballs can block off any Fruit that's between Cherry & Melon, which can open up a chance to take it from him. I do regret to inform you that Jr's B moves by themselves are not as good at building damage as DH's B moves are (unless Customs are on, in which case Side 3 + Up 1/2/3 will wonderfully rack up damage [and staleness]). Jr thankfully is better at KO-ing with them alone than DH is. NAir and especially FAir, as often air-dodged as they may be, will at least hang out long enough to challenge the air-dodges, as can UAir, which is your fastest and most spammable aerial.
If and/or when you DO get in, try to stay on top of him with Side B JCs into aerials that can punish his openings for big damage. However, Pac-Man's Jab, FTilt, DTilt, FAir, and NAir can compete with your own Jab, DTilt, UAir, FAir, and Nair in terms of speed. As least Jr has better approach options and rushdown abilities than his dad. :>