[CateraMV6]

I bet the 3.2L will be easier to swap then the 3.6L because the 3.2L is a modified L81 engine named LA3 and has bigger bore I think... also the electronics you will have to upgrade to the coil on plug design and you may have to play around with the wiring a bit, but as for the DBW, you might be able to get away with using Manual throtle bodies... but then again which ECU are you going to use...
Fitting it wont be an issue, the 3.2 will be very identical, the 3.6 might have some different motor mounts...

Good luck with it all, I hope you find what you are looking for... in the archives...
I would go with the 3.2L personally and a manual swap but thats just me.

I am working on getting the European ECU with a chip in it, and I am hoping I can bump up the HP on mine with at least 20 more...