Thanks for the suggestions all.
The more I think about it, the more I'm leaning towards entering the North Channel from the east (Killarney / Little Current) and poking around for awhile.
My original goal was to define a circular route so that I didn't cover the same waters twice. It sounds as though there is enough variety within the North Channel to do this.
I think I'll order the charts for Northern Lake Huron anyway, just to look at them closely.
1989 Hunter 30'
Southern Georgian Bay
The sea, once it casts its spell, holds one in its net of wonder forever. - Jacques Yves Cousteau