Canons which are FICTIONAL in Carlos' Universe (established)
Star Wars - there are numerous mentions and jokes about Jedi and Sith and the 'old Jedi mind trick' is a standard no no for wizards of his stripe. It's mentioned that one of the Merlin's tactical maps is an effect taken straight from the movies.
Buffy the Vampire Slayer - Thomas Raith is a major fan of the show and there are references aplenty in the books. Specifically, Carlos was able to watch the first two and a half years of the show, but was too preoccupied by his wizardly studies to really absorb most of the end of the third season or beyond so his knowledge there is hazy. Past season five, he knows nothing as the network change from WB to UPN meant that he was unable to watch the show at all since the television he could use in the house (the big tube-based set) did not get that station.
Star Trek - This one is referenced in a few places and Carlos is mildly aware of things Trek-like because one of his sisters is a fangirl. That said, he only knows the broadest sort of stuff.
Firefly - Harry quotes it/paraphrases it ("Thomas is too PRETTY to die.") Also, as Buffy is fictional, I figure it's fair game as it's Whedon. That said, Carlos has no knowledge about it other than scraps and bits of things from one of his sisters. He knows it exists; that's about it.
Monty Python - There are references and also... it's fun. And there really aren't many Monty Python pups, so it shouldn't cause any trouble.
Romero Zombies - Came up.