When I originally switched to REAPER, I used an elaborate method to port my songs out of Sonar, which involved using REAPER's multi-channel virtual ASIO driver, and MidiOX virtual MIDI device. That took me a bit of time to setup and get it so I could in one pass, play the song in Sonar while capturing it all to individual tracks in REAPER.
 
Last night I decided to grab a song I had never moved, and since it was going to be a one time deal, I simply soloed each audio track, one by one, and exported to .wav with names like Track01.wav, Track02.wav, Etc. After exporting all the audio tracks, I did a single "Save As" in Sonar and selected MIDI Format 1.
 
Then in REAPER, I dragged each of the audio tracks over, and lastly dragged the MIDI file, which prompted me to put each channel onto separate tracks, which I did. After that, it was just a matter of putting the drums MIDI clip of data onto my Superior Drums 1962 Ludwig kit track, and setting up the Native Instruments B4 on the MIDI track for Hammond organ. The two MIDI tracks had originally played to rack mount MIDI hardware in Sonar. After all that I added new plugins where appropriate, and mixed the new ported version in REAPER. The song was originally done in Sonar back on 03/14/2004. The end result after porting it into REAPER last night can be heard from the link in my signature.
 
 

For thous who are going to port Sonar projects in Reaper... it is not yet time to start complicated porting. It can happened there will be an easy method, a possibility to just open Sonar project in Reaper. I will let you know separately in case I start work in that direction or there is some show stopper which I have not spotted yet.
 
General show stopper can be legal issue. In my naive imagination, while EULA forbid to do any manipulations with CW software, any output from that software (WAV, MIDI or whole projects) are our and so we can do whatever we want with that (including opening in other DAWs). But I am not a lawyer. May be I have skipped some section of agreement which declare a part of CW software output a property of CW (I mean some parts of the project files). In this case it can be illegal to use these files in other software...
If someone has good arguments or references, please let me know.

When I first switched over to REAPER, I moved all my recent projects, and at that time I used the virtual multi-channel ASIO driver "ReaRoute" that comes with REAPER to move all the audio, and MidiOX to do the same with the MIDI tracks. Back then I had setup a template in REAPER to "Receive" projects from Sonar.
 
My "Receive" template in REAPER had 24 audio tracks pre-setup each on different ReaRoute channels, and 16 MIDI tracks each set MIDI channels 1 thru 16.  All I had to do in Sonar was at the bottom of each track assign the outputs to correlate to the input tracks on my REAPER template. I was also using Sonar as the master MIDI clock, with REAPER slaving to it, so I could put REAPER into record, and it would wait until I hit play in Sonar. Then both would start running, and in one pass all MIDI and all audio would end up on separate tracks in REAPER. It was a chore to setup the template, and reassign all the outputs in each of my songs in Sonar, but for doing many projects, it was the most time efficient way to go at the time.
 
If someone needs to move some projects right now, I can say that both the methods I've described do work, because I've used them both, but if you create an new automated process to move projects from Sonar into REAPER, that would sure be a lot easier than either way I've done it.