If database column bound to the database is boolean type, then the checkbox in the template column will automatically checked.
See my code snippet in this link: http://www.daniweb.com/code/snippet1248.html
In the above code snippet, i have bound a checkbox template column to a boolean field in a DataTable which is created temprorily(not retrieved from database). Change that code slightly to address you requirement.
sorry, i dont quite understand. is there a more simplified way?
on page load, the gridview checkbox item will check those rows that already exist in the database.