Halifax is named after George Montagu-Dunk, 2nd Earl of Halifax, who was President of the Board of Trade when Halifax, Nova Scotia was founded in 1749. Reynolds painted him in 1764. Source.
Edward Cornwallis was Governor of Nova Scotia from 1749 to 1752. The Cornwallis River in Kings County, CFB Cornwallis in Annapolis County, and Cornwallis Street in Halifax were named after him, and a statue (not based on his likeness) was raised to him in Cornwallis Park. These honours are gradually being removed on account of his having put a bounty on the heads of Mi'kmaw people in 1749, after having done the same kind of thing in the Scottish Highlands in 1745. Reynolds painted him in 1756. Source.
Samuel Hood was Commander-in-chief of the Royal Navy's North American Station in Halifax from 1767 to 1770. Port Hood in Cape Breton is named after him. This is a copy by an unknown artist of a portrait by Reynolds. Source.
William Augustus, Duke of Cumberland, was the third son of King George II. He led the government forces at the Battle of Culloden and earned the name "Butcher Cumberland" in its aftermath. He also had command in Hanover and America during the Seven Years War. All of the Cumberland Counties in North America are named after him, including the one in Nova Scotia. Reynolds painted this portrait in 1758. Source.
John Russel, 4th Duke of Bedford, was a member of the British Cabinet at the time of the founding of Halifax, and also a cricket buddy of George Montagu-Dunk (above). Bedford Basin is named after him. Reynolds painted this portrait of him in 1759 or 1762. Source.