The statement that best describes how canon law was used by the Catholic Church to unify people within feudalism is:
It created rules that had to be followed across feudal monarchies if one wished to be a part of the Church.
This reflects how canon law established a common set of regulations and practices that all Christians were expected to adhere to, regardless of the specific feudal lord or region they belonged to, thus helping to create a sense of unity among disparate communities within the feudal system.