Great research, Lionel. It certainly looks possible that William Clucas from the IoM Children's Home was the same person as William Seymour Clucas who married Emily Ruth McDonald.

We have:
1891 IoM census: William Clucas, aged 3, in the IoM Home for Orphan and Destitute Children (possibly born on 18 Nov.1887 in Douglas to a single mother).

1895 April 9, with Home Children on Ship Siberian, destination Brockville Ontario: William Clucas aged 8. ("LDS Family Search site has 1895 as the year he immigrated to Canada.")

1901 Canada census: William Clucas aged 14 is living in Brockville with the Crozier family.

1909 marriage: William Clucas aged 21 to Emily Ruth McDonald (18) in Brockville, Ontario, Canada.

You show Canada/US border crossings for the family.

In the 1920/30/40 censuses William Clucas and his family are living in Milwaukee, Wisconsin, including Canada-born children, and sometimes including McDonald in-laws. William's birthplace usually recorded as England, which was commonly given for the IoM.

Gary wrote that the matchbook, draft card, census records and other data indicate that William Clucas lived out his life in Milwaukee, Wisconsin USA.

Apart from William's "wrong"(?) parents given at his marriage (and there could be good reasons to explain this) all your research seems to fit perfectly.

Sue