The US delegation is headed by Secretary of State Hillary Clinton, her remarks at the conference opening are available (text and video).
UPDATE: Minister Clement's speech text is available - Speech by Tony Clement, President of the Treasury Board and Minister Responsible for FedNor, Presenting the Government of Canada's Action Plan on Open Government. ENDUPDATE
Here's a brief Storify of Canadian-related #ogp2012 tweets for April 17, 2012 (I will update it if there are more):
See previous posts in category opengovca