Why does my audio change pitch upon import?

I don't know why your song is in a different key, but I'm pretty sure that the Key setting is for MIDI only.
Perhaps your project is a different sample rate in Biab and SONAR. But that usually results in audio playing at a different speed, and a different pitch.

There's a setting in BiaB for export as Acidised files when you create audio files of the parts - you need to have that unchecked.  If its checked, then when you import to Sonar, it will retune the acidised wavs to the key set in your project (which defaults to A if memory serves).  If you want to use the acid features, then you'll need to make sure that Sonar and BiaB are using the same settings. 

For me if the sample rate is different it only goes down a whole step,,not a 4th? I guess if you went from 48 to 96 it might be different. But I'm talking 44.1 and 48. 
 
I know a lot of people export from BiaB as midi and OPEN that file in Cakewalk. This allows you to use the better VST's that come with Cake.. If you don't sort this out you might try that.