Yes, yes you can...
Although in active alpha development, my friend at azslow.com has created a plugin that allows Reaper to read the contents of your saved Cakewalk Sonar projects and open them in Reaper. I have been using the open Alpha for a while and have been happy with the results.
Follow the information here:
http://www.azslow.com/index.php/board,13.0.html
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