This is my problem with Smash 4 -- someone has an issue and people immediately say "pick another character".
While I understand the game can't be balanced, it's disappointing to see people jump the character ship so freaking fast when a "flaw" arises.
As far as projectiles, see what you can do about reading when Toon Link is going to go for an arrow as well as what his preferred movement methods are.
For a slow and fat character, it's incredibly difficult and quite possibly one of the most tedious things in the game, but with your speed, I'd think you could shorthop the arrow and possibly be able to punish him for it.
Also, try catching his bombs and using them yourself.
For boomerang, I'd see about getting behind him so you don't have to worry about an approach getting interrupted by its return, not to mention the hitstun's enough to where he pretty much gets rewarded no matter what he chucks at you, so don't spend too much time trying to intercept his stuff with SHFF'd nairs and the like unless you feel that you have to.
I don't play Falcon in Smash 4, but your tilts should have enough range to force him into shield at a decent distance, allowing you the chance to better pressure him without having to worry about him launching another projectile.
The best advice I could give you is attempt to stay as close as you can, even if it means just crossing him up with jumps -- the more you stay on him, the less he feels it's safe to throw something else.
I know very well that it's not easy (trust me), but I've come to learn that it's what works for me, so I hope it works for you.