I've never understood why scanning and hybrid discussions are so disliked on this forum. This forum has a gallery, every image posted to it was scanned or digitized somehow!
To answer the OP's question, definitely stick with Nikon since you already have the right lens for the task at hand. Any of the bodies selected will work just fine.
Don't worry about pixel count. Remember that 1080p (typical screen resolution) is only 2MP, so even on a 12MP camera you're going to be doing a lot of downscaling to make it fit on a modern screen.
As for which one, if this was a dedicated scanner replacement, I'd say get a D200 (I can find them locally for under $200Cnd) and be happy with that. Since this is also a fun camera, size and handling become important. I don't know anything about the Fuji. The D300 has cult status (I lust after one for absolutely no good reason) where the D200 doesn't, but both are "studio" cameras; thus larger and bulkier than the D3200, but they give you full manual controls and a better view finder. If you go all Auto when playing with your not-film cameras, get the D3200 and call it a day (great images, lousy manual controls).