Depending on how many 3rd party plugins you might have and how co-operative they are you may find the following useful. If it doesn't apply to you feel free to ignore it or use only any bits useful to you.
Having both the 32 and 64 bit versions of SONAR on the same computer doesn't of itself cause any problems. Many of us run multiple version in both 32 and 64 bit without problem.
Problems can however occur when you tell SONAR to scan for VST plugins. when running 64 bit SONAR there may be 32 bit plugins that you want to run because a 64 bit version doesn't exist yet. That means having to scan the location where those 32 bit plugins are as well.
That's not a problem either except that when using 32 and 64 bit versions of SONAR you may want both the 32 bit and 64 bit version of particular plugin so each program can make use of it. The rub is that some plugins don't behave and you end up with both the 32 bit and 64 bit version being scanned by SONAR's VST Scanner and you have 2 of that plugin appear.
I have an additional folder just for 32 bit (x86) plugins for those where the manufacturer wants to always install both a 32 and 64 bit version. When it works properly then the 64 bit VST scanner doesn't load the 32 bit version but when it doesn't work properly it means I end up having 2 of the same plugin where the 32 bit one is also running through Bitbridge. For those plugins only I use the 3rd folder. Working out which plugins don't cooperate has to be worked out by trial and error.
To get around all that I have my system setup as follows.
1. Program files\Cakewalk\Vst Plugins\Manufacturer\plugin
All 64 bit Plugins
2. Program files (x86)\Cakewalk\Vst Plugins\Manufacturer\plugin
All 32 bit plugins you want to run in x64 because no native 64bit version exists.
3. Program files (x86)\Cakewalk\VST Plugins(x86)\ Manufacturer\plugin
All 32 bit plugins for which you already have 64 bit versions and the VST scanner insists on installing the 32 bit version as well under bitbridge giving you 2 copies of the same plugin in SONAR's Plugin manager.
SONAR x64 scans 1 & 2
SONAR x86 scans 2 & 3
Apart from folder 3 the others are all default locations if you allow SONAR to just perform it's normal installation.