Living in MI for at least 25 years, I would say it's hard to tell what the weather will do. I would maybe wait until May and whenever you decide to go....be prepared for rain and/or cold temps. There is a saying for around these parts...."if you don't like the weather, wait 10 minutes---it will change".

For example....I got married last year at the end of August on Mackinac Island (near the U.P.) on a Saturday...Friday was 75* and sunny, Sat (the big day) was 52* with rain at my outdoor wedding and Sunday was 80* and sunny....go figure. The weather here is finickey. Be prepared for anything is my advice.