The 'ballast' thing is as a couple of people have said - timber ships began carrying people from Britain and Ireland to Canada, rather than making the westward crossing in ballast. As one New Brunswick writer put it in his 'Strangers from a Secret Land', the Atlantic crossing became profitable in both directions. There was a huge surge in emigration from Britain and Ireland in the years after the Napoleonic Wars, often (but not always) subsidised by the local authorities.

re English emigration to Canada in the early 19th Century, another shamless plug...........see my article 'Southern England and the Mania for Emigration, 1815-1840' in the British Journal of Canadian Studies, Vol 16, no.1. The whole edition is given over to English emigration.