Sioux Lookout is in the Kenora District; the Gen Web site is: http://www.kenora.net/district/
If your ancestors are hugenots, then the original spelling may be Dupuis, and you can only guess how many English spelling variations of the pronunication of a French name there might be (i.e. Depue). Land grants were given to many British subjects who fought on the British side of the American Revolution and then came to Canada. Some of the indexes of the Land Grants books are online: http://www.ogs.on.ca/ogspi/uclandv3.htm
You can try searching for relatives through Canada 411:http://canada411.sympatico.ca/eng/person.html
and writing to ones who live in the general vicinity of Sioux Lookout. By obtaining a copy of your father's birth certificate, you can try working backwards to find a marriage certificate for your grandparents, which can help lead you backwards to a location to search for in the 1901 census.