Copied from an entry on my blog from Blogger: http://1234works.blogspot.com/
Perry the Platypus and Candace Flynn are my favorite Phineas and Ferb characters. And no, I'm not gonna pair them up just because they're my top 2. It's just a coincidence. I do like their connection, a special one that is.
I happened to be interested since Perry seems to be more involved with Candace than Phineas and Ferb (not counting the fact that his battles against Dr. Doofenshmirtz made most of their inventions disappear). The scenarios involving Perry and Candace that I remember are Perry appearing in Candace's bedroom in this episode where some of the big focuses are Candace hates Perry but actually shows that she loves him when he disappears, Perry and Candace switching brains, and Perry dreaming of Candace dreaming about Phineas and Ferb get busted.
There are some fan theories that says that Candace's dream from "Wizard of Odd" is also Perry's. There are some evidence of this, like the dream having Agent P, Dr. Doofenshmirtz and even Major Monogram. And it also appears that there's a Perry POV there too. I think every scene in the episode would have either Candace or Perry. Also, when Candace wakes up, there's also Perry lying beside her.
Not only that, in "Does This Duckbill Make Me Look Fat?"; the episode which Perry and Candace switched brains, the song "Perry the Teenage Girl" is supposed to describe Perry, though the traits fit with Candace as if she were a secret agent as well. In "Gaming the System", the ball gown Perry wore after being struck by the Ball Gown-inator is surprisingly huge for him, and it totally fits Candace. While when Phineas, Ferb, and Isabella were struck, their dresses fit. Not to mention that the dress Perry and Candace wore also looked good on them, as said by Dr. Doofenshmirtz and Jeremy.
There are a few theories around this special relationship between Candace and Perry. Some say that Candace and Perry are mind-linked, some may think that Perry is Candace, and I think it's that Perry is Candace's father who really cares about her. Aww...