I'm not sure about the term “look better”. I think maybe the nuance is that the entrenching of a domestic right compels Canada towards a duty, in this case to provide access to clean and safe drinking water.
The domestic law proposed in say, amendment G-1, clarifies that duty in a crisp way. The inference around the international law is less binding in terms of its compelling nature on the duty to provide access to clean and safe drinking water in first nations land.
I would say that one is more of an international recognition of Canada's commitment in the international space. The other is entrenching a domestic law that compels Canada to essentially provide duty.