Never believe everything you read on census, the information is only as good as the informants knowledge or who fills that information in. Its not unusual for people to claim they were married or widowed when they were not.
John Mason made a few declaration of intention - 27 March 1922 - says he is not married
2 November 1936 - says he is not married and no children.
Eventually natuaralised 18 September 1939 - petition 199167
In original post you say quote "I have located a marriage record for a Jack Mason and Eleanor Laing in Ontario"
Where/What date is the marriage of Jack Mason to Eleanor Laing -
Sandra