I lived in South Haven, MI for several years with little knowlege of Chicago's fishery. On the other hand, the fish migration up the coast i can. April may be a little late for the Walleye, but coho salmon should be near St.Joesph, MI or similar across the lake. Chicago or slightly north. Brown Trout are always a possibility along w/ steelhead samon. Wind direction plays a major role for water temp. and depth of bait fish, therefore, depth of salmon and lake trout. I phoned a former MI neighbor and he suggested the captain in the link below. Sorry I couldn't share more related info. http://http://captainalscharters.com
Coho in the 2-5 lb range as well as some steelhead. Perch fishing is also a possibility. The big salmon and lake trout come later but you should be able to get fish weather permitting. Good luck and remember to post an AAR.