Come to Michigan! With Easter falling so late, that's actually a pretty pleasant time of year to do the Lake Michigan coast - shoulder season rates make the resorts far more affordable than in the summer, but the weather is generally nice enough for hiking and outdoor fun and the flowers and forests are just starting to show their summer colors.
I personally love Traverse City and the Leelanau Penninsula in April, lots of wineries and trails and lovely restaurants, but if you don't want to drive that far, there are a lot of nice stops on the southern part of the lake. Grand Rapids has a surprisingly nice zoo and art museum for the city's size and the Frederick Meijer gardens are beautiful, the tulips in Holland will likely be starting to bloom by Easter, and there is a state park with sand dunes and walking trails near Saugatuk that I used to love as a kid (though I haven't been there in years).