There doesn't seem to be a marriage of John Shewan to Mary Jane Bent in the England and Wales marriage index. Pity, because if there had been it would have told you the names and occupations of their fathers.
The 1901 census lists John Shewan, born April 18, 1847 in Scotland, immigrated to Canada 1860, with wife Mary J and four children aged 8 to 23, all born in Ontario.
The IGI lists one John Shewan, born in Scotland on 18 April 1848. I have found it not unusual that birth dates in the Canadian census are a year out. This John Shewan was the son of Alexander Shewan and Eliza Chalmers, and he was baptised in New Deer on 26 April 1848. I think this is the one you should be looking at.
There's a family in Old Deer in the 1851 Census consisting of Helen Chalmers, widow, 67; Christian Chalmers, sister, 60; Eliza Chalmers, daughter, 31; granddaughter Ann Keith, 9; grandson John Shewan, 4; and granddaughter Elspet Shewan, 2. You can view a transcription at
https://www.freebmd.org.uk/cgi/search.pl.
In 1861 Helen, Christian, Eliza and Ann were all still in Old Deer, Christian now described as sister-in-law rather than sister.
I have not found Elspet's baptism or the marriage of Alexander Shewan to Eliza Chalmers.
You can view John's baptism record at
www.scotlandspeople.gov.uk. This may tell you that he was illegitimate. If so, it would be worth taking a look at the New Deer and Old Deer Kirk Session records, which, if they survive, will probably contain a report on the matter. They may also shed light on the birth of Elspet Shewan and Ann Keith. The Kirk Session records are only available in certain archives in Scotland at the moment, but rumour says that they will become available on Scotland's People.
If John immigrated to Canada in 1860, he must have gone with members of his family as he would only have been 12 or 13 in 1860.
Note that in both 1881 and 1901, the census says that Mary Jane was born in Ontario, of English origin. This probably explains the absence of a marriage in England
