It would be a less challenging trip to go via the Erie Canal and Hudson River. The St Lawrence route gives you access to some fascinating places to sail but it is not a casual undertaking (distance, fog, currents, cool weather, isolation).
Unless you're looking for a long, costly (both time and money) adventure, have it professionally transported to the Cape.
If you want a bit of adventure and to save a couple bucks, have it dropped off somewhere along the way. For example, Oswego, NY would be a good place to start from. From here you could join the Erie Canal and enjoy some beautiful scenery and a relaxed trip on your way east to the Hudson.
If time is a problem, consider dropping your boat off in Catskill, NY. This will cut way down on the distance you'll have to travel to the Cape and will certainly help reduce your transportation cost.
If you'll be cruising around Dennisport, you're probably familiar with my old homeport of Sesuit Harbor. Thirty years later, I still miss it.
If you're really going to sail the boat, I'd recommend the Erie Canal and Hudson river as it cuts out a lot of distance. The Erie Canal does require that the mast be unstepped and stored on deck though.
As pointed out previously, trucking it the distance may be less expensive, and certainly faster.
If de-masting to go the Erie route, I read an account of one boat that was very glad that they had the mast shipped on ahead, rather than dealing with it lashed to the deck. Something to think about.
If you have the time to enjoy the sail I recommend you run the North Passage from the Soo around the Canadian side and down through Georgian Bay. Also, see Pictured Rocks National Seashore east of Munising in Michigan's upper penninsula. When you pass through the Soo you might like to see the sea-plane museum. You can choose to sail past Detroit through Lake St Clair or take the Severn Canal from the foot of Georgian Bay to Lake Ontario. (check the mast height and fees before you begin this one). Passing through Lake Erie there is a marina right at Cedar Point Amusement park. A popular port is in Put-In-Bay in the Erie islands - look for Perry's Monument and have a Frosties for me at the foot of the state docks. Erio Ontario has a nice cozy little public dock on the Canadian side and There are places to dock frequently along the US side. Most of the clubs I know in Cleveland will extend you a welcome. See the Flats on the Cuyahoga River. Its been a while but there were a lot of night clubs there when we lived in the area and some offered valet parking for boats. There are many books about navigating the St Lawrence and the locks around Niagara Falls. The Thousand Islands area is famously beautiful and a very popular cruise. At some point you will have to decide weather to take the Erie canal or exit to the Atlantic at Nova Scotia. You will probably want to take the canal. Otherwise, Quebec is one of the nicest tourist destinations I know. I've heard many nice reports of navigating the Erie Canal; an adventure in itself. Lots of books are available on this.
This is not a short trip. You could run it in a summer if you have the time. You could do it in stages and put the boat up for the winter almost anywhere along the way and pick it up again the next season. This could be an opportunity in a lifetime for a really memorable cruise in relatively protected waters where help is near and you can get to know your boat.
BTW - our boat is in Muskegon Michigan. We look forward to extended Great Lakes sailing and exiting the St. Lawrence onto the Atlantic for blue water cruising as our retirement.