Mexico's President Felipe Calderon and Argentina's President Cristina Fernandez de Kirchner (R) attend the opening plenary session of the G20 Summit in Toronto, Ontario, June 27, 2010. [Agencies]

US President Barack Obama (2nd L) and Canadian Prime Minister Stephen Harper (2nd R) confer with White House Chief of Staff Rahm Emanuel (R) and Michael Froman (L), deputy assistant to the president and deputy national security adviser for international economic affairs, at the start of the opening plenary session of the G20 Summit in Toronto June 27, 2010. [Agencies]