FWIW, in most Canadian History curricula for secondary schools in Canada, you would find mention of ships carrying timber from Canada to Britain and bringing Irish & Brit emigrants back for several decades at least ... But as ballast? That sounds more figurative than literal, to put it charitably.

Because of their numbers, their poverty, the cold, the economic conditions, and the fear of disease from the ships, Irish immigrants (those who had survived the voyage) often had a very hard time of it in Montreal. Most cut out for the States pretty quickly. However, many did remain and became assimilated into Quebecois society.

You may have heard the poignant emigrant song Andy Irvine recorded, which recounts a gruelling voyage, at the conclusion of which, the emigrants, as they come ashore in Quebec, are greeted by hordes of Irish beggars ...