Sorry that I cannot directly answer your question, but this map (link below) on the Library and Archives Canada site could prove useful to you should you obtain more information:
http://collectionscanada.gc.ca/pam_archives/index.php?fuseac...Click on the image icon and then on the subsequent page, click on Image 2. That will provide you with a map that can be enlarged and dragged around. There are many named islands in Cowper Township, though I can't detect one that is named Timothy Eaton Island. You may want to take a closer look yourself.