I don't know if this helps, but here are all the black Hensons who were living in Ontario in 1861 (from "Blacks in Canada, 1861," by Barry Noonan):
Kent County, Harwich Twp, p. 15

HENSON, James, 57, b. USA, laborer, Wesleyan Methodist, black
... Atha 50, b. USA, mulatto
... Mary Jane 14, b. USA, mu
... Topiter 11 (no idea of sex), b. JSA, bl
... Oliver 8, b. USA, bl
... Katherine 6, b. UC (Upper Canada), mu
... Charles R. 3, b. UC, bl
... Margaret M, 1, b. UC, mu

....................

Kent County, Township of Camden & Gore, p. 49
HENSON, Isaac 36, b. USA, farmer, Methodist, black
... Harriet 22, b. USA, mulatto
... Willis 3, b. UC, mu
... Annie 1, b. UC, mu
Also living with them, Aman Davis (no idea of sex), 20, b. USA, Methodist, black.

...................

Kent County, Township of Camden & Gore, p. 50
HENSON, Peter 21, b. UC, farmer, Baptist, black
... John 70, b. USA, bl
Also living with them, Elijah Osberry 17, b. UC, Baptist, black.

............

Grey County, Owen Sound, p. 6
HENSON, James 61, b. USA, laborer, Wesleyan Methodist, black
... Missa 20, b. USA, bl

.............

Kent County, Township of Chatham and Gore, p. 44
HANSON, John 72, b. USA, farmer, Quaker, black
... Leah 47, b. USA, Wesleyan Methodist, mulatto
Also living with them, Maria Smith 22, b. USA, Roman Catholic, black; Peter Cord 15, b. USA, servant, no religion, black; and Edward Gance, age unable to read, b. USA, Baptist, black.
................

As with all sources, it's always best to refer to the original source versus just this transcription. I don't know if any of these Hensons are related to Josiah, but it's a start.

Good luck in your research.

- Lisa B. Lee
Oakland, CA