A few comments for you if you have made the choice to go north and west via Lake Superior. There are no such things as sea dragons (or so I'm told), and people do sail on Lake Superior, but some warnings are worth while even to ocean sailors.
We have a storm season here on the Great Lakes too. The weather gets noticably more changeable, both in the speed at which fronts come through, and the severity of the changes, starting in mid-September and getting worse from there on in. October is getting cold and rough, and November is what we call the gale season - after that ice along the shore becomes a problem. You'll want to be at Thunder Bay by mid-Sept. I've come across Lake Superior in an autumn gale in a 650 ton ice breaker and had a snotty ride, and a Contessa could have had a desperate time of it.
I know you folks sail in the North Atlantic, and you'll have plenty of miles under your keel by the time you get to the Great Lakes, but this is a different environment than the ocean (not to say better or worse, just different). The problems here are the increasing speed at which weather systems move through the area late in the season, and the way that weather systems happen to collide over the lakes. Fall storms sometimes don't give much warning and Superior can see waves in excess of 20 ft. high due to the strenght of the winds, but because the fetch is so short (compared to the ocean) the waves build unbelievably quickly and never get to lengthen out. You end up with tall, steep waves on a short period (frequency). They could be very difficult to ride out if you are caught out.
One thing I've observed is that, for the area where I live (Georgian Bay), I can get a good idea of what's coming in the weather by listening to the weather observations for the areas west of me because most of our weather tracks west to east. For example, what's happening in eatern Lake Superior and Whitefish Bay will usually find me about two days later. For Lake Superior try monitoring conditions in Lake Winnipeg to get a heads up on what you might see in the near future. The real weather bombs happen when a warm wet system comes up from the Gulf of Mexico and crashes into an arctic air mass moving in from the west, and they seem to do that now and again directly over Lake Superior for some reason. Locally the MAFOR forecasts are usually pretty good but the broadcasts always include the disclaimer "winds and waves may vary considerably due to shoreline effects".
Other than that, you'll see some gorgeous cruising grounds especially if you get into the area known as the North Channel in northern Lake Huron. Superior is majestic, perhaps partly because of its unpredictable strength.