On November 8, the Michigan Secretary of State released an initial list of presidential primary candidates. In Michigan, only the Republican and Democratic Parties have a presidential primary. The Secretary of State is required by law to choose candidates discussed in the news media. She chose four Republicans and eighteen Democrats. This story has the list.
Anyone who was not included can still petition, but needs about 11,000 signatures. Any registered voter can sign. Thanks to Thomas Jones for the link.