Welcome to the forum and congratulations on the new-to-you boat!
It has been a very long time since I made that trip so take my notes with quite a bit of prejudice. There really aren't route options, head north along the St Claire River, keep heading north until you get to Tobermory then turn right until you get to Owen Sound
The currents in the St Claire River can be a bit challenging so plan a little extra time for this portion. I was heading from Tobermory south and it did add a couple knots to our SOG at times. I don't remember Goderich at all, looks like you draw 6ft, you may want to verify depth before going in. I do remember stopping in Kincardin but not the details of the harbour. My memory from 30 years ago is getting a little foggy. I was recently in Port Elgin looking at a boat and it does seem like a very nice harbour with some amenities. A bit of a hike to town for provisions.
Tobermory is an absolute must! Wonderful little town and Little Tub is a very protected harbour in the middle of the action, at least what there is of it in this small town. I haven't sailed along the west coast of Georgian bay but once past Tobermory there look to be a lot of wonderful little places to stop and you may want to take your time along this portion.
If you are from Owen Sound I'm sure you are familiar with the fantastic cruising grounds all around Georgian Bay. If I had an extra week or two I would make a detour to the North Channel on the way, maybe even circumnavigate Manitoulin Island.
Most importantly, keep us up to date on your planning and take lots of pictures to share with us
I just realized you will be coming from Michigan. You will likely need to clear into Canada in Sarnia so this would be a good place to stop for provisions before heading into Lake Huron where the next easy grocery stop will be Tobermory.