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
'Nautai te salutamus!'