I read a book about a London rake who was sent to Scotland to pick from three sisters to be his bride from a marriage agreement made by his father and the girls father. Out of the sisters one of them does not want to marry the man so she dresses and acts horrible. The man picks her anyway and finds out later that she is really pretty and suits him great.

I think the name of the book is Midsummer Magic by Catherine Coulter. The story follows exactly what you described. RNRG