I believe that answer would be no. Sonar relies on stuff (API's, etc.) that is specific to Windows in order to function the way it does. I remember reading somewhere about attempts to run it under WINE, but it was an unsuccessful mess. I don't expect that Cakewalk will port it to Linux anytime soon, which is fine. Let them keep developing this into a more superb recording package. I'm guessing that getting it to Linux would most likely require a rewrite of the code from ground zero. I hope they don't waste the development time and continue to put their full resourced into Windows. I use it in Windows XP Pro and it runs superbly - with only a few minor tweak to the OS that were made.
I do know that some audio interfaces run under Linux - RME comes to mind as well as M-audio stuff.