These are dangerous times. Nuclear weapons are proliferating among tin-pot regimes around the world, from North Korea to Israel. 
Canada has substantial quantities of important resources that nations are known to fight for, such as hydrocarbons and fresh water.
Canada's nearest neighbor is a nuclear powered state with a leader who claims the right to attack other states at will.
In my opinion, a properly responsible government of any country is justified in seeking nuclear deterent capability. States with special strategic needs such as Israel, Iran, North Korea, and Canada especially. 
I think the different handling meted out by the US vis a vis Iraq and North Korea shows distinctly that a nuclear deterent is effective.
If the nuclear non-proliferation regime was holding up, I would agree that adhereing to it is the responsible approach, but since it's not holding up, I can see no advantage in being the only sheep among the wolves, so to speak.
Nukes for Canada!