Final answer:
Dundurn Castle was built by Sir Allan MacNab, a prominent Canadian politician, and was completed in 1835. It is located in Hamilton, Ontario and serves as a historic site available for public tours.
Step-by-step explanation:
As per your question, Dundurn Castle was built by Sir Allan MacNab. It was not built by Justin Trudeau, John Maclachlan, or anyone else. Sir Allan MacNab was a prominent Canadian politician who served as the Premier of the Province of Canada before Confederation. Dundurn Castle is located in Hamilton, Ontario and was completed in the year 1835. It is a neoclassical mansion that has since been restored as a historic site and is open to the public for tours and events. Dundurn Castle reflects the grandeur of that time and the influence of Sir Allan MacNab in the Canadian history.