Bucket is pretty safe against Mario even if he approaches with them. Just release it in his face right when you catch the fireball. Watch Nintendude's match against The Doug from CW6 for an example. I don't know if Mario players have come up with new technology since then, but it should still work against most Marios.
I can't really give you a lot of advice about the Peach matchup, but it does help to be able to catch her turnips, especially if you can glide toss. But sometimes she'll bait you into catching her turnips while recovering, which might still be better than getting hit but leaves you with fewer options. Instant tossing might help with that, but it's not something I've practiced. She is very light and floaty, so she dies off the top early to dtilt, usmash, dsmash, or even fsmash. Gatling probably works on her and might kill starting around 50% (just a guess). On the other hand, she can't kill you off the top very easily unless she catches you with an uair or lands an usmash somehow. Watch out for the floating dair edgeguards. I think you can avoid them by sweetspotting, but if you miss you're going to eat a nair and probably die. You can try to mix up your recovery timing to throw her off, but she can do it on reaction so it's better to recover high if possible.
Ganon's kind of a weird matchup. Worse Ganons are super easy, but better Ganons are really tough. Unfortunately the best Ganon in TN lives two and a half hours away so I don't get to play him as often as I'd like.