The sepoy mutiny of 1857, also known as the Indian Rebellion of 1857, took place during the Governor Generalship of Lord Canning. The mutiny was a significant uprising against British rule in India and had widespread consequences for both British and Indian society.

Option 1: Lord Dalhousie was the Governor General of India from 1848 to 1856. Although his policies, such as the Doctrine of Lapse, had an impact on the social and political climate leading up to the mutiny, he was not in power during the actual event.

Option 2: Lord Lytton served as the Governor General of India from 1876 to 1880, which was after the sepoy mutiny.

Option 3: Lord William Bentinck was the Governor General of India from 1828 to 1835. He was not in power during the time of the sepoy mutiny.

Therefore, the correct answer is option 4, Lord Canning.