1. Ancient Greek: In the context of ancient Greek history and geography, the pronunciation is MY-see-uh. This is the traditional pronunciation based on the Greek language.
2. Modern Greek: In modern Greek, the pronunciation is mee-SEE-ah. This is closer to the modern Greek pronunciation of the letter "υ" (y) in the word.
So, if you're talking about the ancient region of Mysia in Asia Minor, then MY-see-uh is the correct pronunciation. If you're talking about the modern Greek word, then mee-SEE-ah is more appropriate.