This blog only mentions US records when of potential interest for Canadian, British or Irish genealogy. The new U.S., Social Security Applications and Claims Index, 1936-2007 is such a case.
Unless some of the information is embargoed you may find: applicant's full name, social insurance number, date and place of birth, citizenship, sex, father's name, mother's maiden name, race/ethnic description (optional).
A substantial number of the 49,416,104 records of people in the databse are for immigrants. Searching the database for birthplace Canada yields 489,007 results; for United Kingdom 407,242 and for Ireland 192,656. It's not that many, there are obvious errors, perhaps as many as 20%. Still, that would make it 54th in Ancestry's list of Canadian databases.