Generally in MI, parents are given joint legal custody with primary physical custody going to the mother unless she is proved to be unfit or does not want custody. I have gone through two MI divorces with kids and my first ex tried to fight me for custody of our son because he did not want to pay child support. At the first hearing the judge told him he was giving him very liberal visitation which was every other weekend and two evenings a week.
Unless they've begun doing 50/50 recently - I don't think you have much of a chance to get that without the mother consenting. You should however not worry about her getting sole custody, it should end up being joint so you both have the same rights to the kids medical, schooling and other important decisions in their lives. Even with me living in Florida with my children, I still share joint custody with their fathers but I have physical custody.