Immediately after the first race riot in Canada, which was a reaction to the attempted return of runaway slave Solomon Moseby to the United States, the Canadian government received a request in 1837 for the extradition of another Kentucky escaped slave, Jesse Happy.
Happy had escaped four years earlier, and the horse that he had ridden away on had been left on the U.S. side of the border. Happy had written his former master, David Castleman of Fayette County, KY, telling him where to find the horse. In the U.S., stealing, in this particular case horse-stealing, was considered a serious enough offense for Happy to be returned to Kentucky.
But that was not so in Canada; the matter was forwarded to the Law Officers of the Crown in London, England: "Since slavery did not exist in Canada the crime of escape could not exist there and the use of the horse in Happy's case had been to effect escape and not for theft." Happy was not extradited to Kentucky and remained free in Canada. No other extradition requests for runaway slaves were made to Canada until after the Ashburton Treaty (1842) was settled between Britain and the U.S.
For more see pp. 170-171 in The Blacks in Canada: a history, 2nd ed., by R. W. Winks; W. R. Riddle, "The Fugitive Slave in Upper Canada," The Journal of Negro History, vol. 5, issue 3 (July 1920), pp. 340-358; J. M. Leask, "Jesse Happy: a fugitive slave from Kentucky," Ontario History, vol. 54, issue 2 (1962), pp. 87-98; and J. H. Silverman, "Kentucky, Canada, and Extradition: the Jesse Happy case," The Filson Club History Quarterly, vol. 54 (1980), pp. 50-60.