Editing stereo files is a lot easier if you don't have to create a Cakewalk project and then open it up and place your wave file in there. In programs like Cool Edit and, I think, Wavelab, you just open the wav file. In addition, stereo editors are designed from the perspective of editing stereo files. DAWs are designed from the perspective of multitracking. There will be features and UI differences in stereo editors that are condusive to stereo editing, and the same applies to the DAW. So, no, there probably aren't specific tasks in Wavelab that are impossible to do in Sonar; it's just that they'll be a lot easier to do in Wavelab.