I'm not good at passenger lists but maybe someone can try to find a James Bushnell between 1904 and 1915 on an incoming passenger list to the UK to determine when he arrived back in England. He may not have stayed in Canada long and that could be another reason he didn't show up on the census.
The 10th Royal Hussars
With the outbreak of the Second Boer War, the regiment sailed for South Africa in 1899. After fighting at Colesburg, the regiment participated in the relief of Kimberley in Feb 1900, the Battle of Paardeberg immediately afterwards and then two years of fighting in the Transvaal. If your James Bushnell is the one listed above with the 10th Hussars, you may get info on him at the archives.