Ganon is absurdly easy to combo as Fox or Falco. If Fox gets a grab on Ganon at low %s, it's pretty much done right there. You can get 2-3 uairs in a row off a uthrow. That's a lot of damage, and on some stages (YS anyone?) it's a stock. What's even better is Ganon is easy to waveshine. A waveshine is a free grab on Ganon. Dair -> waveshine -> grab -> uthrow, then proceed to juggle. Ganon's recovery is predictable, too. Shinespike it, or interupt it with bairs. There's absolutely no reason for Ganon to make it back if he's off the stage. You're a hell of a lot faster then him too, so as long as you're smart enough not to walk into his attacks, you should be fine. Try some simple wavedash and dashdance games (like dash towards him and WD back to see if he'll whiff and attack, then go in for a grab, a shine, or an aerial).
As Falco, You can shine -> dair -> utilt at least. Even if he DIs the shine, you can chase with lasers and get back on top of him quickly. PILLAR against Ganon too! It completely shuts down his "gtfo" aerials out of shield that tend to **** Falco if he hits you with them. As for SHL, remember that Ganon has no projectiles. Any time you arent right next to him, you should be shooting lasers. It's that easy. If he jumps onto platforms, follow him with fulljumped double/triple lasers. Don't forget that you don't have to approach him ether! Falco's lasers allow him to control the pace of the match, aswell as his opponent's playstyle. If you sit there and spam lasers, Ganon has to come to you. Your control over the stage is an 11 out of 10; Ganon's is a zero, especially against Falco. Use that laser, and show him you aren't taking **** from him. That's YOUR f*cking stage, not his.
Now I'm not a Shiek player, but I know she can CG Ganon quite severely...but so can he! So be carful around him. If your friend dosn't CG, more power to you. Get a grab in, CG for a while, then just kick his *** with tilts and aerials (sounds like how Shiek plays every match...). Ganon is a good weight to juggle as Shiek, and you can edgeguard him really well thanks to, once again, his predictable and slow recovery. Not much else to say here.
As Marth, it's a bit tough. Ganon's range is almost a match for yours, so your spacing needs to be flawless. However, you can combo Ganon like a beast with your utilt and uair(
Lol, like this). It's pretty easy to combo into a dair or an fsmash too. You're quite a bit more maneuverable then he is too, so it comes down to a game of wether you're good enough not to walk into his attacks or not. Try to make him whiff his aerials (which are usualy followed by jabs, so be carful. You said your friend dosn't L-cancel though, right? If not, don't worry about the jabs. They won't come out fast enough), then dashdance into fairs or a grab or something. You can also attempt the spacing game against him, but like I said, you don't severely outrange him like you do most other characters, so that can backfire.
Try this stuff

I'm no pro, but I have a Ganon playing friend, so I know what he's like to play against.
EDIT: If you didn't already know about shieldgrabbing, then I agree 100% with the post under mine. Shieldgrabbing allows you to punish almost anything that hits your shield, from any smashes to shffls to dash attacks. If your friend dosn't l-cancel and plays Ganon, you have AMPLE time to shieldgrab him any time he hits your shield with an aerial.