Prime Minister Netanyahu of Israel (which has a nuclear arsenal) warns the UN about Iran (which doesn’t). Last week Canadian negotiators helped sabotage the idea of a nuclear arms ban in the middle east.
The Canadian government has offered no reason, but informed speculation is that it appears to be at the urging of Israel. Of course, Israel still refuses to admit that it has nuclear weapons and missiles to deliver them. If a nuclear-free zone in the Middle East is created, Israel would have to reveal its nuclear arsenal.
According to the Guardian, Netanyahu personally thanked US Secretary of State John Kerry for intervening to protect Israel. It is not known whether he also called Mr. Harper.
The move which is a reversal of Canadian policy, has caused consternation among many former Canadian diplomats. One retired diplomat sent a scathing email to the Foreign Affairs department asking for an explanation, copying many others.
“Please explain why you would jeopardize Canada’s longstanding policies on nuclear non-proliferation on the basis of a totally biased policy supporting Israel,” he demanded.
Iran has declared that it is in favour of a nuclear-free Zone in the Middle East.
Canada Talks Israel/Palestine 
the growing influence of the Israeli lobby on Canadian foreign policy is cause for major concern. It is a retrograde foreign policy in almost every respect.
Canada has now made a statement about its vote. But the argumentation is a bit convoluted.
http://www.international.gc.ca/media/aff/news-communiques/2015/05/23b.aspx?lang=eng