The Welland Canal is big and I think exciting. You have to have a minimum of 3 people and need good sized fenders. Sometimes there are people available at both ends to hire for transit help. The huge size and lift of the locks is fun. You have to start through when they say and can't stop until you exit the canal. That may mean a 6 PM start and finishing at 2 AM. You have to be alert for big freighter traffic at all times, particularly at night as some of them don't have lights on their bow and the bow can be a hundred yards in front of any visible lights.
I agree that you need to check height clearance and draft for the Erie Canal from Lake Erie to the Oswego Canal. The Erie Canal clearances are much better from the Oswego Canal to the Hudson River. The Oswego Canal needs a height clearance on under 22 ft. I believe. We did it at 20 ft.
The 1,000 islands area is fun too, and you'll be close. Watch the charts carefully when you're not in the big shipping channel as the water levels are way down there too and some of the marinas are not accessible for larger boats. The marina at Brockville, ON, about 50 miles up St. Lawrence Seaway from Kingston, is very nice and you can walk to all the downtown shops and restaurants, etc. Check drafts and large boat docking before going. If no space at Brockville, anchor out and dinghy in the the city docks. You can also just anchor out in the St. Lawrence far away from the ship channel where there is good depth in the river and there are lots of nice little islands you can dinghy to on the Canadian side near Brockville. Some can even take larger boats.
BTW - If you have not done the Trent-Severn, that should be on your to-do list also.
Doug