Lynn
This is a CD Architect file. It can't be opened in Sonar. You can do all the necessary editing within CDA.
I doubt it. Someone who does not know what a .cda file is probably does not have CD Architect.
Most likely the OP has tried to use windows to copy the contents of a playable audio CD, and has found he has a bunch of short files with the suffix .cda. The .cda (Compact Disk Audio) file is not data, but is an index that tells Windows where the audio track is located on the CD.
If you want to edit or play an audio CD file from Sonar or other audio programs, you need to "rip" it. There are a gazillion free CD rippers, and Windows Media Player will do the job as well.
http://windows.microsoft.com/en-us/windows/rip-music-from-cd#rip-music-from-cd=windows-7 http://www.techsupportalert.com/how_to_work_with_audio_cd_cda_files.htm