denverdrummer
Just figured out my issue. Right click on the desktop and go to "screen resolution"  then click on "Make text and other items larger or smaller"  drag the slider all the way to the left (smaller), and you should be back to full screen rez in Sonar.
 

Hmm, it seems like the issue is that SONAR X2 is different than SONAR X3. I'm assuming that your workaround is affecting both at the same time? If so, then Badmrpotato's issue may be different. Not sure though. 

Well, whaddya know...I just upgraded to the new X3c and bada boom bada bing...fixed.  :)  Im back to the full resolution...yay!

Glad to hear that! 

I assisted someone several years ago that was killing their four displays when opening SONAR. It would turn off three displays and revert to a single display. The single display would then display everything in 16 bit colors.
 
Turns out it wasn't a setting on SONAR.exe, but rather a result of the VST Scanner scanning a plug-in that was triggering Bitbridge.exe that had it's Properties (in Windows) set to "Settings - Reduced Color Mode - 16-bit color".
 
Took us about 4 hours to isolate it. No idea how that got set like that.
 
Anyhow, moral of my story is that I wonder if somehow a component that SONAR was scanning was set to use reduced colors. Glad it's solved! If it happens again, try disabling the VST scanner and see if the results change. If so, go through all of your plug-ins and see if you can find the culprit.

Interesting fix.  I wonder if I go back into my screen settings to set the screen magnification back to medium and install X3c if I'll get the full 1080p display in Sonar.  I haven't loaded the C-patch yet, so I'll try this tonight when I get home.

Confirmed that my issue was different.  I went back to the medium magnification settings and installed X3c.  When I opened the program Sonar still acts as if it were on a 720p display.  So it looks like you need to make sure to turn off all magnification settings or you will lose screen real estate.