I will provide a brief answer to your question about what is preventing the creation of a national strategy in Canada: it's a lack of political willingness. One of the problems is that there aren't enough people to demand this kind of strategy, because of the stigma related to suicide in our society. It's only recently that people have dared admit that they were suicidal or that they needed help. Because the demands are so few, measures in that respect are considered less profitable than others, politically.
The prevention of mental health problems and intervention are inevitable when we talk about suicide prevention, but they are not the whole strategy. There are many other measures specific to suicide. That's why we need a national strategy.