From the Article:
$1:
Prime Minister Stephen Harper is off to New York City and Pittsburgh this week to hobnob with world leaders, but he won't address the opening of the United Nations general assembly.
Foreign Affairs Minister Lawrence Cannon will deliver Canada's statement to the 192-member assembly Saturday evening instead
There is no issue here. This is the usual process. Unless you have something very significant to say that effects most of the world there's no reason for a country's leader to personally address the UN.
Recent world leaders who addressed the UN were, for example, Bush when he was trying to convince the world that there was yellow cake in Iraq (hardy har har) and trying to get everyone on board with that, and then Chavez when he stood up to announce to the world that he had read a book.
Can anyone really think of anything pressing Harper had to address the world with? I can't. So I'm not seeing the controversy here and I'm pretty sure I wouldn't see a controversy if it was a Liberal or NDP leader in the PM's chair right now.