Christiana Stewart married William Fidler in Charlottetown in 1849, and moved to Sunbury County, New Brunswick around 1857. An Adelaide Stewart from Georgetown PEI married James Fidler, a widower with a son born on the Island, in Fredericton New Brunswick in 1862, and moved to the same parish of Sunbury County, New Brunswick.
Adelaide Stewart was not in New Brunswick at the time of the 1852 census. This scenario makes more sense if Christiana and Adelaide were related, and Adelaide met James Fidler when she moved to New Brunswick with a sister or cousin.
By 1861, there were, in Sunbury the following Fiddlers:
William, b. England 1823, his wife (b. PEI) and family - eldest son b. PEI
William's father John, b. England about 1799
William's sister Mary, b. PEI 1846 - this is perhaps Mary Jane Fiddler, who married Robert Betts in NB. Her parents were John Fiddler and Hannah Offer
James, b. PEI 1828 - possibly a widower? with son James, age 1 born PEI
George Fiddler, born England
Edward Fiddler, b. 1826 England in next-door Chipman
Christiana's son Thomas named two of his daughters Christiana and Adeline.
James Fidler and Adelaide Stewart had three children.
George Fidler married Janet Humphrey from PEI, and moved to Sunbury County NB. Adelaide Stewart Fidler's second husband was David Humphrey from PEI - they were married in 1869. Again, it makes more sense if there was a connection between Janet and David Humphrey. From census records, David Humphrey was not in Sunbury County until Janet Humphrey moved there as well.