With the infinite, there's absolutely no hope, absolutely none. Without it, there is. 35:65, a **** matchup still, but no, not unwinnable.
Advantages: Superior range, mobility, KO power, survivability, **** CPs.
Disadvantages: Damaging chaingrab that sends you offstage, grab range when the grab is so deadly, equally **** CPs.
Summary: I'll keep it short. You can space bairs against D3's grab. It's not that hard. Mix in a dash of downB because it can annoy him. In the air, you win, so go at him with bair. Play really, really patiently. Jumping in head-first like you may be accustomed to will just get you *****. If he's offstage, gimp with bair, if he ever has to use up B, just hit him away at the peak of the jump or on the way down. Keep him offstage without his jumps and you may not get a gimp but you will get a bunch of damage.
Aerial Game: You win. His bair is good, but yours is better and your aerial acceleration and speed are way better, so space bairs on him.
Ground Game: You still win. DownB and ftilt are way better than his ftilt and dtilt. if he ftilts, you can shield and dtilt, ftilt or shieldgrab if you dashed in.
Approach: Don't if you don't have to. PS his projectile, it's easy. If you do have to..Well, merlin help you, dawg. You COULD use up B and wear his shield down, but you better hit it with all of the hits.
Camping Game: He will camp in his shield and you won't like it. You will camp with bair.
Edge Game: His isn't that great vs you but he can bair your up B for a solid gimp. Beware. Use bair to gimp him.
Surviving: He will kill with utilt, stay to his side and he may have trouble. He can dtilt you at the edge for a kill at like 180% after a CG.
Killing: It's hard, but your best chance is to force him into it by getting him offstage and forcing him into up B. Threaten an edgehog and you can ledgehop a reverse punch for the kill.
Stage Striking: Strike FD and SV, try to get to Yoshi's or BF.
Stage Banning: Tough one. He can go RC, but for a good portion of that stage he can't CG very well, it's not so hard to avoid it. Only problem is on the boat, he can always get you. You can get him too of course but yeah it's a problem. I'd say ban delfino for the walkoffs. If he chooses castle siege, be glad.
Counterpicks: Brinstar and Japes are good. Mansion to a lesser extent but on mansion he will have a really tough time killing you. It won't be legal though generally so yeah.