Actually, the Welland is not the only way to get from Lake Erie to Lake Ontario. You can take the Erie Canal from Buffalo eastward to Oswego, NY. Of course, you'll have to lower the mast at Buffalo, but there are a couple of marinas there that will do that for you. The trip itself is a wonderful canal trip and you can usually put in along the way for no cost. Once you get to Oswego you'll have to have the mast put up again, and that also will cost you. Do a google search for Erie Canal for info.
Remember that you'll have to pay about $20 per lock on the Welland, and there are something like eight sets of locks to go through. They will take either CAN $20 or US $20, and since the Canadian dollar is worth less than the US dollar it will pay you to have the money in Canadian bills. Whichever way you go it is going to cost you some money to get through the canals.
I suggest you stop a few days at the Lake Erie islands -- South Bass (Put-in-Bay) is great, at least on the weekdays -- too much partying for me on the weekends. Also, if you pick the wrong weekend you'll find it hard to find a spot to moor or dock your boat because of the crowds. If that happens go to Middle Bass, just to the north of South Bass. It has both a state park with docks, and a yacht club that will allow you to berth for a small charge. I prefer the yacht club (Middle Bass Island Yacht Club), but be nice to the dockmaster!! Kellys Island is also nice, a lot quieter and family oriented than South Bass.
I would stop in Sandusky. You can go to the Cedar Point Marina, but Sandusky has many different marinas, the handiest being Battery Park. If you belong to an ILYA yacht club I'd look into the Sandusky Sailing Club as you'll get a nice discount there. Go to www.sanduskysailingclub.org
for more info. There is a lot to do in the Sandusky area and a lot happening on the waterfront -- many different marinas there if you don't want the sailing club.
Wherever you go and stop you'll have a great trip. Enjoy it and be safe. If you get to Sandusky send me a private message on Sailnet as I keep my boat at the Sailing Club.