Hi Rebecca,

BiaB has got a feature to do that:

"Generate Synthetic Vocal
Your Melody or Soloist track with lyrics can be rendered to a vocal audio track by sending it to the 3rd party vocal synthesizer Sinsy.

To access this feature, you should first pick a song that has lyrics and a Melody. If no Lyrics are present, you can still generate a vocal synth using the syllable of your choice (la la la etc.)."

The vocaloids sound better IMHO. If you want to compare Sinsy and a vocaloid you can use following links:
https://soundcloud.com/boehmusic/artificial-voices-sinsy
https://soundcloud.com/boehmusic/artificial-voices-gumi-version

I hope that helps.
Guenter