Scottbr is right. Anchorages on the Canadian side of Lake Huron are top secret. There are rumours that they exist but then there were similar rumours about WMDs (see "Off Topic" for THAT debate!)
The only achorage that I know of would be in the lee of Lyal Island at Stokes Bay. It is a fair way in on the curve of the Bruce Penninsula and I haven't stopped there. I have it in my GPS if the weather kicks up and I need a safe haven but that hasn't happened so far.
Unless you do a Sarnia to Tobermory Run, there are no other anchorages that I know of.
Grand Bend - Very few transient slips. Likely too close to Sarnia for a first stop. Grand Bend is a summer party town if that is your thing.
Bayfield - There are several marinas in Bayfield and an excellent marine shop if you are in need of repairs or supplies. The Village of Bayfield is very pretty with some fabulous restaurants and shops. (but who cares about that, we're sailors arent we!)
Goderich - This is a bulk freighter port with recreational slips. You can get in there safely even under the worst conditions. I've never stopped there so I have no opinion on the harbour.
Kincardine - Nice harbour close to downtown. One of our favourites.
Port Elgin - This is a great harbour with a very nice beach and summer events in the park. It is a kilometer or so to walk to the main street if you need provisions. It is slightly indented in the curve of the Bruce Penn and adds an hour or more to our straight run from Bayfield to Tobermory.
Southampton - There is no longer a harbour in Southampton that can take anything close to a 42 footer with 5'6". Port Elgin is the only option there.
Next stop - Tobermory.
Kincardine and Port Elgin are not expensive. I'll check my log and post the per foot rate we paid last year.
Ports Guides are very good. Richardsons will also show you there are no chartable safe anchorages along the Cdn side. Someone with fantastic local knowledge may be able to find a place in the Fishing Islands... my view - abandon hope all ye who venture there!