I think Sonar by default will load a 64-bit version of a plugin that had been initially loaded as a 32-bit one, when both plugin types are in the search paths. I am not 100 % sure of this, but it is dimly lighting up some synapses in my dusty old brain.
There might be a parameter for you to specify the action to take, where you could have it load the 32-bit versions, if desired, but I would think you would want to perhaps accept the missing plugins messages, then swap 64-bit versions for the missing 32-bit ones.
Would that work?
A long while back, when I moved to a 64-bit Sonar, I did my very best to leave 32-bit projects to continue to open in a 32-bit Sonar (projects with 32-bit plugins loaded), and if I created a 64-bit project, I only loaded 64-bit plugins into it, so I never really had the nightmare of the crashes a lot of folks had early on, and I also made a deliberate decision to use only 64-bit plugins from there on out, other than a small number of 32-bit ones that seemed to work OK in 64-bit Sonar, where there was no 64-bit plugin version available. Whatever the worth, most of the plugin makers released free updates for purchased plugins to give folks 64-bit versions, and I would suggest you go through that exercise too.
Hope some of the above is of use to you - best of luck to you with it all.
Bob Bone
Bob Bone