Mario and Roy are both really fun to play (and can be really frustrating to fight)! But in my experience playing as both characters I would say mario has the better matchup.
Long Range: Roy does not have a projectile. While Roy is fast, he will potentially have to deal with fireball camping, which can be annoying to deal with... -1
When Roy is at
Mid range from Mario I'd say Roy has the advantage. Mario has a projectile in his fire ball, but it has landing lag and with Roy's speed he'll be able to punish it easily. Not only that but Roy has a disjoint on all of his moves so he can out space Mario +2
Close Combat: Roy has much worse frame data than mario. Mario's slowest aerial comes out at frame 16, but Mario will very rarely use his forward air in close combat. Mario's Neutral air comes out at Frame 3, U-air is frame 4, D-air frame 5, and B-air frame 6. Roy's fastest aerial is his U-air which comes out at frame 5, but is not necessarily his best. On the other hand, Roy has his incredibly powerful sweet spot which can really put on the damage and push Mario far enough that it can get him back into the mid range. Just try not to get comboed... the fast falling does not help. -1.
in terms of
edge guarding Mario... It's going to be pretty hard especially considering the speed of mario's up-B. But Mario's recovery move has about the same range as Roy's. If you can catch Mario's second jump you're good, but it's going to be hard to catch Mario while he's recovering.
I haven't played against Mario on enough stages, but Mario thrives on the platforms on Battlefield and Dreamland, and he can use them to extend the already long combos he has against you. Final destination, while there's not way to mix up your recovery/landing, with B-reverses and fastfalling you should be able to get back. And Mario can't extend his combos high enough to kill you off the ceiling.
In my opinion:
Advantage-Roy: Final Destination, Smashville
Advantage Mario: Battlefield/Dreamland, Town and City, Delphino plaza
I'd say the match up is
55:45
given that MArio can combo Roy into oblivion, but Roy can kill mario really early