Most of Zelda's ground moves beat every option G&W has. They clank his moves, then continue to hit him through it. Her F-Smash is what she's going to challenge you with, so be very careful about approaching from the ground unless you think you can sneak in a D-Tilt before her hitbox can come out. Never approach her from the top. Her Up-Air is enormous and can even beat out G&W D-Air. Her Up-Smash stays out for a long time and comes out pretty fast, so she pretty much has an impenetrable defense from the top if she's expecting you. You can mess with her by throwing out a Down-B stall on the way down to her, but be careful with this since her Up-Air is really scary.
Her aerial options are very weak if you are already grounded. Her N-Air and Neutral-B don't cover anything below her, so she is very susceptible to pressure from underneath her since her D-Air covers just about nothing and is unquestionably beaten out by G&W Up-Air. As long as you can maintain good positioning, Zelda's only way to escape your pressure is with an Up-B. She'll have a difficult time doing this due to the 32 frame startup and will remain combo food until she gets a break to complete her animation. She's extremely floaty too, and a decent string of Up-Airs can kill pretty much everywhere but Dreamland. FoD is usually my go-to pick for this matchup.
Bucketing Din's is usually pretty safe to do if she's trying to play campy. I can't figure out how to do it twice on the same one, but it does play a significant role in the matchup. Keeping two charges is enough to KO her in most situations and stages. Having just two means you still get to keep your stall mindgames along with your charges, since you'd be emptying your bucket if you tried to stall with 3 charges. Dump it on her from a read on her teleport.
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A good Samus is extremely annoying to deal with for sure. Fortunately, her Super Missiles can be ducked under during neutral so it isn't as bad as it could be for most other characters. She's just as floaty as Zelda and is just as susceptible to dying off the top as her, but she is not as easily pressured by G&W Up-Air because she has Down-B as an option. If she's coming down, harass her with single-bacons until you can get her into hitstun, then try to whack her with the pan if she's in reach. The pan's semi-spike is good for KOing her most of the time since it removes her tether recovery when it sends her below ground level, and her vertical recovery isn't quite enough to make it back most of the time.
Keep your distance in neutral, her grab is ridiculous when you're both on the ground and often leads to some deadly followups. When she's on the ground you will primarily want to approach her from a diagonal angle with a F-Air. This isn't going to be safe all of the time if she shields it, so I've found that the best option is to read the shield and respond to it by jumping over her and crossing her up with a B-Air, rather than coming from the front with F-Air. It will often pressure her shield enough to hit her out of it, so it can be quickly followed up by a D-Tilt, which can then be followed up by whatever vertical combo fits your fancy. Another option is to grab her through shield since yours comes out way faster. I like Battlefield for this matchup.