Here is something kinda fun ... a site called "Automated Geneology" that has transcribed and put online a searchable database of some census years 1901/1906 some parts/1911 and some farther back ... I remembered it and went in to search the last one done for public access. An amazing project they've done in this transcribing/uploading for free access to the general public

I searched 1911 for Kingston Ontario ... a list of about 22 Donaldson's came up, but no Thomas. Maybe he wasn't born yet? What exact YEAR was it that your grandparents married (when Grandpa listed age 35 at marriage) ? I don't recall you mentioning the year. Knowing would narrow the year/timeframe.

http://automatedgenealogy.com/census...Id=86&geosort=

Anyways, a good and fun site if you're into tracking backwards for geneology searches once you get some names going. Geneology is ADDICTIVE!