I believe openers should be natural, based on observation. I can't buy into the concept of canned openers. I do not want to approach a girl and open with some random question that I got from some existing pool of openers that I don't really care about the answer too.
At the same time, I have always been shy and had difficulty with small talk and it is my belief that natural openers are essentially "canned" openers that one has developed through years of life experience and the practice of engaging people. Natural openers are "natural" yet "canned".
So, if one practices canned openers over and over, I guess they eventually become natural openers, based on the idea that they are ingrained and can be adapted to the situation.
For example, I used to feel weird and uncomfortable saying "How you doing?" to people. It was a premade line that I though was silly. But eventually, I just started saying it, and now it is my "natural" way of greeting people and I don't even think about it.