It looks like the 1851/52 census entry Karen found could still be your William. I found the marriage registrations for some of William and Mary Ann's children and they born in Peel County.
In case you don't have the marriages, here's what I found in the Ontario marriage database at Ancestry:
Alexander Hamilton, 26, cabinet maker, born Bolton, Ontario, son of William R Hamilton and Mary Anne Temple married Isabella Nickle, 27, born Paris, Ontario, daughter of Thomas Nickle and Isabella Fair on 22 Jul 1880 in Walkerton, Bruce County, Ontario. Witnesses: Fred. Wm. Hamilton of Teeswater and Elizabeth Nickle of Walkerton.
Williamina Hamilton, 21, born Chinguacoosy, Ontario , daughter of William R and Mary Hamilton married George E Wakefield, 21, butcher, born Puslinch, Ontario, son of George and Phebe Wakefield on 20 Feb 1883 in in Teeswater, Bruce County, Ontario. Witnesses: W.A. Wakefield and Marion Hamilton, all of Teeswater.
Marion Hamilton, 28, born Bolton Village, Ontario, daughter of W R and Mary Hamilton married Walter J Coates, 28, merchant, born Clinton, Ontario, son of William and Sarah Coates on 21 Oct 1885 in Teeswater, Bruce County, Ontario. Witnesses: Robt Coates of Clinton and Lizzie Hamilton of Teeswater.
Edmund Hamilton, 22, cabinet maker, born Teeswater, Ontario, son of William and Mary Hamilton married Annie Roos, 20, born Preston, Ontario, daughter of Charles and Bridget Roos on 13 Oct 1885 in Galt, Waterloo County, Ontario. Witnesses: F.W. Hamilton of Teeswater and F.C. Roos of Preston.
Jacquie