Here is what the newly updated Birds of North America Online says about the migration routes of our Upper Midwest loons:
The loon populations of the Upper Great Lakes in Michigan and Wisconsin migrate along the southern Great Lakes and use an overland migration route to the Gulf of Mexico (Alabama east along the Florida coast) and e. Florida. Some individuals stage on lakes along the way and even over-winter in larger reservoirs in Tennessee (Kenow et al. 2002) and Alabama (Belant et al. 1991). Minnesota and Wisconsin breeding populations have two migration routes, and both generally use the Great Lakes as staging areas. The primary route includes the Gulf of Mexico from Mississippi west to Texas, and the second documented route uses the southern Great Lakes to make an easterly migration to the mid-Atlantic.
Last year's chicks are on the Gulf right now--loons spend 2-3 years in saltwater before heading to their breeding grounds. This year's chicks...I don't know how they can possibly survive this.