Relationship of International Law and Municipal Law — Treaties — Effect of treaty on interpretation of statute — Administrative law — Effect of treaty on exercise of discretionary powers — Immigration — Deportation of parent with Canadian-born dependent children — Status of ratified but unincorporated treaties in Canadian law — Convention on the Rights of the Child — Effect on municipal law — Whether Convention created legitimate expectation that best interests of Canadian child a primary consideration — Object and purpose of international and domestic legislation safeguarding rights and interests of children — Whether immigration officers having to take best interests of Canadian children as a primary consideration — The law of Canada