How much time do you have? Ever been to Boldt Castle?
If you don't mind a trip, maybe 1.5-2.0hr trip over to Alexandria Bay... Boldt Castle is a must see, stop and take the tour. Bad part is you'll have to check in with imigration (office is at castle) then again when you arrive back in Canada.
If not, take a ride up under the Canadian span 1000 Island Bridge, a lot of beautiful new homes around that area.
We were in Kingston Saturday, nice place. The canons were kind of neat, but nothing else really sticks in my mind.
If you ever get a chance, have lunch sometime at the Kingston Brewery (no not a liquid lunch). A was a very unique restaurant, we had lunch in the courtyard.