Check out the District 9 US Coast Guard Webpage. They have a list of the icebreakers that work the lakes in this area:
http://www.uscg.mil/d9/D9Units.asp
The "Katami Bay" based out of Sault Ste. Marie is the one that does work in your area. The Sault Ste. Marie Sector's responsibilities cover all of Lake Superior, and the northern sections of Huron and Michigan, it seems:
http://www.uscg.mil/d9/sectSaultSteMarie/