Fine, and good enough. Most sites are bouyed and the ones that I have gathered seem to not fit your criteria. Most are at or near the 100' max you also asked for. (I by no means have them all) The bad news is that the one I would most likely have suggested (besides the Islander) is up the river, thus asking where are you staying? (in relationship in miles to Alexandria Bay)The Robert Gaskin is outside of Brockville, can have a steady current if the locks down river are opened, about 100-200 yards off the shipping channel and in 70' of Canadian Water. It looks like Brockville is a good haul by boat from Clayton.
I might have suggested you hook up with Abucs Scuba and dive for the day with them. Abucs is in Canada but it is approx. 45 mins over the boarder. I might also suggest that you contact Mo Hunt Charters out of Clayton and speak with those guys as to good sites (Mo also maintains a small shop in A-Bay directly across the park where the wreck of the Islander is...)
I may have also suggested contacting Aquarius Charter (aquariusdivers.net ) in the 1000 islands based in Clayton and see if thet can direct you...
Now if you had bothered to alter your question and directed regarding the Islander I may have told you that it is simplily the easist wreck shore dive you will ever do. As soon as you hit the water from the entry point start decending, in about 3 kicks you will see the wreck in 60' +/- of water. (well with in your range of "newer" divers) If you are going to be that close and want to get a quick dive or two in then this would have been the place to do it. Swimming either direction from the wreck (East or West) there is some interesting geological features and tons of fish. And in the years before the Hospital (which is right next door) used to toss their old medical bottels into the river. Occasionally people find some pretty rare bottles there.
This is as best as I could have done...