Weellll... I'm not sure if I can properly settle this debate!
The pronounciation depends on who you ask in my family - my Dad's side is Welsh/English, so my Great Grandma had me as a Meeegan, and my mom's side (and I think the more typical Canadian way of saying it) pronounces it more like Megan with first syllable "May". When I was living in New Zealand for awhile, it was back to Meeeegan. I emailed my dad years ago from New Zealand to ask him, when they named me, what pronounciation did they intend? My dad said that's why he nicknamed me Fred. lol

So there you have it.

Not sure if you can get Mig back on that one!
PS I think the most adorable thing ever, is hearing my nephew call me Auntie "May-ten" because he can't get the "g" sound just yet.