Samus is heavier than Ganondorf. As for anti-space animals strats...
I don't think it's that bad of a matchup, really. Haven't played much Ganon versus Falco, but I've got quite a bit of experience against Fox (Thank you Chester, you shine-happy *******. May you die a horrible death). Anyway, I think the most important thing to know is that you've got the range advantage. In the air, pretty much all of your attacks outrange those of Fox, leaving him with very little counter-attacking possibilities, unless you mess up with L-cancelling or something. Anyway, aerial down+A will set Fox up for combos and, when shielded, will knock him out of shield-grabbing range if you spaced it correctly. Don't overuse it though. I like catching people who're running in with a dash attack or grab by short-hopping over their head and landing with the spike, then following with a second one to knock them back down. If they fail to tech or if they use their rising attack, you've got 2 more free spikes in for a ridiculous amount of easy damage. Of course, your opponent will adapt very fast (if he's any decent) and start rolling away right after the second one. That's when you try to guess which way he'll roll and follow with a forward air, or a wave-landing and a ground attack. He'll soon adapt to that too and start shielding your attacks, but that's when you replace the ground attack with a grab... Anyway, this is just some mind-game theory, find what works best for you. One thing I recently noticed in my playing against Fox is that, for some reason, I always throw him up. Maybe it's just a natural reaction since he's a fast-faller. But anyway, always throw him down. It'll pop him up nicely to follow with a neutral A or a forward tilt. The down tilt can set him up for combos as well, but it's easily seen coming and crouch-cancelled, so use it sparringly. Use the ground neutral A a LOT, since it's one of Ganon's few moves which can compete with Fox's arsenal in terms of speed. Always try to follow a blocked aerial attack with a neutral A, kind of like with Fox's Shine. It'll usually stop him from countering with anything. The forward tilt also has very good stats all-around, and has no counter when spaced properly.
Aaaaaaaaaaaand I think that's it.