I can definitely understand how people can struggle with the match up, here's my advice: learn the rest setups, ganon is hella easy to rest cause hes really big, hes heavy, and he's not a floaty. My go-to setups are uptilts, falling up-airs (and regular up airs), and pound. All of these can lead to guaranteed rests that aren't terribly hard to execute. HOWEVER ganon does have one of the best rest punishes in the game, his up-tilt, but you really shouldn't let that scare you off from trying all the rests you can, cause that's the only way you'll get better at hitting them. What I do as shield pressure a lot is falling up-airs (if you catch them with it, free rest) then fall next to them and try to shield poke with an uptilt (you actually have a better chance at poking ganon from behind, and an even better chance when they are facing the left.. I think.) This gives you two opportunities for rests, with almost no risk involved.
In neutral with ganon, you have to play pretty safe, since if he reads your movement, its not hard for him to jump fair you. I usually space bairs, once one lands, just take use your frame advantage to pressure him more, or keep him where he is. Stage control is also very important. If you have center stage you shouldn't over-commit with anything, just keep him caged in that corner until he makes a bad decision trying to get out, and punish him accordingly.
Edge-guarding is very simple, yet very crucial. When hes off stage, I highly recommend chasing him with bairs/fairs. If you can get a good bair on him when hes far off stage/with no jump, that could easily be the stock. If you wait to hit him till he's near the stage, he'll probably live and get another chance, and the situation will reset giving more opportunities for you to **** up/him to find a way back on stage. All I really use for edge-guarding is bairs, fairs, f-smash (sometimes dash-attack) when I'm on stage, and an occasional dair from ledge when I'm in a bad situation. However, this is all for gimping, but if you can force him to up-b on stage, GO FOR THE REST.
Another note is that ganon's down-grab leads to a guaranteed fair or bair, depending on which DI you choose, so keep that in mind.
Hope some of this helped!