Welcome to Sailnet. You may wish to post this question in the Lake Huron forum under "Destinations".
I sailed from Midland to Bayfield Ont 2 years ago stopping in Thornbury, MacGregor Harbour, Lions Head, Wingfield Basin, Cove Island and then a straight overnight run to Bayfield.
So what?, that wasn't your question.
I know there is a well marked inside passage through the 30,000 islands up the east side of Georgian Bay with many stops along the way for provisioning and anchoring. I would strongly recommend buying the Ports guidebook for Lake Huron which includes Georgian Bay and the North Channel. It has excellent descriptions of what you are looking for.
Once in the eastern end of the North Channel, the main provisioning stop is Little Current. It has everything you would need. Killarney is a good stop for fuel
, pumpout, ice, laundry, beer etc but groceries are marginal. Gore Bay is apparently good for provisioning but I haven't been there.
Start a new thread in the Lake Huron Destinations forum and you'll get lots of enthusiastic advice. I know several of the people who have posted there regularly are from the Midland Penetang area.
See you up there in July!