-Pepper Ann/ Doug Funny: Both shows featuring two teens high school trying be cool, but one of these shows is better than the other (honestly I feel that Pepper Ann is what Doug should have been). Story could feature either main character moving to either one's high school as both can help each other out (like Pepper can help Doug be more cool and Doug can help her in turn with whatever he can help her with). Their friends can be included too if you wish.
-Kim Possible/American Dragon: Kind of like the same premise as before or either one can meet on location during a mission. It be a good and interesting mix of science meets magic.
American Dragon/Danny Phantom: It seems almost everyone has thought about this one but here's my pitch:
Danny Fenton and his class travel to NYC for a field trip until he catches wind of a ghost on the loose, 'going ghost' after it. He comes across Jake and both have a little scuffle and both end up loosing the ghost. The ghost (be someone from the show or otherwise) turns out to be a goon working for two of the main villains from both show (maybe Vlad Plasmus and Fright Knight with the Hunts Clan or Aragon and Fright Night with the Dark Dragon) as they come up with a plan to takeover the city/world with the spirits of the underworld as our two heroes work together to save the day.
Danny Phantom meets the Ghostbusters: just use your imagination 😉👌