William and his brother Robert Graham Dunlop shared a home near Goderich, at Gairbraid (now known as Saltford, Ontario). Being both bachelors and unaccustomed to domestic work, they sent home to Scotland for a housekeeper. Louisa McColl arrived in Canada to take care of the two brothers. Shortly after, tongues began wagging and it soon became clear that Louisa's situation was insupportable and she would need to either marry or leave the country. Robert and William decided McColl was irreplaceable and tossed a coin to see which brother would marry Louisa. William supplied the coin and Robert lost the toss; after the wedding it became known that William had supplied a coin with the same face on both sides. Robert never objected.