I do not know what do you mean by "1000 islands open"?
I know one boat cruise company in Brockville will be open for 1000 islands. I called them today. They will have One Hour cruise at 10am, 1pm and 4pm tomorrow. Their phone # is 613-345-7333 at Blockhouse Island, downtown Brockville. You can call them tomorrow to confirm. The price is $12 each person.
My friend told me the cruise boats at Kingston are better than Brockville. I do not know if it is true. Try using google to search and call them tomorrow.