looks like it's wav only... Thanks.

You can import MP3s into your project and export them as 16bit 44.1 wave files. Then you will be able to burn the Wave files to CD.
 
Other tools like Media Monkey and VLC do not require you to convert MP3s before burning CDs.
 
To use the Sonar Audio CD Burner, your feed files must be 16 bit 44.1. If you use Media Monkey, you can burn CDs directly from 24 bit Wav files (no idea if it dithers). 
 
http://en.wikipedia.org/wiki/MediaMonkey
 

Great! thanks!!

If you purchase the MP3 encoder from Cakewalk you can burn MP3 CDs.
The other option would be to download the free Lame MP3 encoder and manually install that to Sonar and use it to make your MP3 CDs.  
 
Search the forums for both and you will find lots of information.
 
Peace

+1 for Lame. I use it. I've never paid for the Sonar MP3 encoder. I find the Lame encoder better than most others I have tried.