I don't think the declaration in itself opens up anything that wasn't already there. If a case can be made that a particular treaty is flawed or not complete, or historical evidence can demonstrate that a treaty was negotiated on the basis of misunderstandings, or anything of that sort, those kinds of assertions and arguments can already be made in Canadian courts. Whether or not they succeed would depend on the evidence and what lies behind those negotiations.
I don't think this declaration changes or adds to that. It simply says that the important rights indigenous peoples have to land and resources need to be respected, and that will be a bit different in every national context.