I misunderstood your original comment Mark. To move to a Mac, I’d simply resync with the Evernote servers after installing Evernote on your Mac. I think I had set up my encrypted container before I started using Evernote on my Mac, and pointed the database to the container in Evernote’s settings (this was before I started using Espionage).
You’d use one method (sparseimage) on Mac, and another (TrueCrypt) on Windows. The database on each computer would stay in sync by syncing with the Evernote servers- they wouldn’t really see each other at all, even though they’d stay up to date with each other each time you sync with Evernote’s servers. Maybe I’m still not understanding your question. If so, let me know.