The French version of Michael is Michel (MEEshel.)
I understand where you are coming from, but just to offer a counterpoint: unless you (a) are anticipating living in a trilingual community and (b) really have a problem with names being mispronounced, there is no need to worry about finding a name that works perfectly in all languages. Of course it's nice when it works out, but if you love a name, you can just work with it.
My name is virtually impossible to say in Spanish, but when I lived in South America, everyone managed. My DS' name is a Scottish family name; I (French-speaking with DS) and everyone in our French community handle it just fine. (Most people just say it with a bit of an accent.) I will also point out that Quebecois and Acadians are very familiar with Anglo names, so I really would not worry about your MIL. Michael is a common name -- I would be shocked if she couldn't pronounce it.
FWIW, when fed Michael, Nymbler suggests a few names that work in all three languages: Simon, Thomas, Daniel, Ivan, Nathaniel, Mattias (? not sure how those last two would work in Spanish.)
professor & maman de DS1 (6) & DS2 (1)