I don't know but I'm guessing Allison Stoner because she is the voice of Isabella. Good question. Sorry I couldn't quite help but I'm guessing her.
Vanessa is voiced (and sung) by Olivia Olson.
Doofenshmirtz
Melanty Weleanor sings "The Only Fish For Me" from Phineas and Ferb.
Phineas, Ferb, Isabella, Baljeet and Buford were all shown in the video, However, Olivia Olson, Who voices Vanessa Doofenshmirtz, sang the song.
Ferb and Vanessa
Vanessa Doofenshmirtz on the show Phineas and Ferb is voice acted by Olivia Olson.
vanessa's boyfriend
Yes he does. He married Vanessa but vanessa also have a crush on Johnny her classmate.
Vanessa Doofensmirtz
vanessa's boyfriend
Vanessa is voiced by Olivia Olson.
Olivia Olsen plays Vanessa Doofenshmirts
Well, Ferb does take a liking to Vanessa, Doofenshmirtz's daughter.