The Security and Prosperity Partnership of North America summit in Canada released a plan that established U.N. law along with regulations by the World Trade Organization and World Health Organization as supreme over U.S. law and set the stage for militarizing the management of continental health emergencies.
-Worldnetdaily.com, Tuesday, August 28, 2007 by Jerome R. Corsi
As the question above states, Is a presidential agreement the same as law? Looking at Article I, Section 10 we see reference to "treaty, alliance or confederation." This has lead many to believe that the Founding Fathers considered there to be different levels of agreements with foreign powers. However this clause starts with "No State." I am of the opinion that this limits the states from entering foreign agreements.
As for the Federal Government we need to look at Article II, Section 2, Clause 2 that states that the President "shall have Power, by and with the Advice and consent of the Senate, to make Treaties." This requires Senate approval of all Treaties. The debate has been on the levels of agreement that do not require Senate approval. Basically the pattern has been if the agreement is within the scope of law passed by congress than no further approval is needed. However anything outside the scope of existing law requires approval.  
In Article VI, Clause 2 Treaties are given the same weight as law passed by Congress and signed by the President. This is why I believe the Founding Fathers, though they did not comment much on the subject, determined that the Senate must approve all Treaties, seeing that they gave ALL legislative authority to Congress.
So, if the President is agreeing with Mexico and Canada to supersede US Law with regulations from the World Trade Organization and World Health Organization, isn't this a legislative act that requires the vote and approval of both houses of Congress or is it a Treaty requiring Senate approval? Can a President replace US Law with the law of a foreign body without Congressional approval at the very least?