I needed another instance of Sonar (one instance for live keyboard midi rig, another instance for live recording) so I installed X2 (64bit) AFTER installing X3 (32bit) and X3 (64bit).
 
The two instances work well together using the same interface (X32Rack 32 channel USB card).
 
But now my project files all changed to X2 icons, and launched X2 by default.
I fiddled with regedit and got the the project files to launch X3 by default.
 
I did get the project icons to stop showing X2 icon, but now it is just generic icon.
How do I get the project files to show the X3 icons? 

If you haven't yet patched X3 to X3e, the patch will reset the associations for you.
 
Otherwise:
 
Control Panel > Default programs > Associate a filetype....
 
Scroll down to .CWP, click the change program button, and SONARPDR.EXE with the X3 icon should be shown right there in Recommended Programs alongside the current X2 icon - Select it and OK. You'll want to do the same for CWB and CWT types, and mayeb old WRK and TPL types if you have older Cakewalk project and template files around.

The change program did not work, even if I browse to exact SONARPDR.exe file. That is why I used regedit. Regedit corrected the association (I double click a .cwp file and Sonar X3-32bit now launches as I wanted), but even though I found icon assignment in regedit, and made the logical edit, the icons changed from X2 to generic icon.
 
So file association is fixed (using regedit), but icon is not. I am stumped.

I am not at the computer but made a post a couple months ago on this if you can find it. It requires a registry edit.

I bumped the thread instead.
 
Edit - finally at a computer again so can get the link http://forum.cakewalk.com/FindPost/2977009