Thousand Islands - book early! Or stay in Watertown, Alex Bay is only about 25 minutes from there.

Other ideas, if they have their act together by then (anyone know?) ROC operates a Fast Ferry across Lake Ontario to Toronto.

ROC and BUF also have great minor league stadiums if you are into baseball (Rochester Red Wings and Buffalo Bisons)

Chautauqua Institution is another great suggestion. There's always something going on there, check out the schedule on their site.

Finger Lakes also great for wineries!