Is Enlightment ultimatelly up to you (Karma and Freewill)? According to the traditional Buddhist dogma the fourth noble truth or eight-fold path is the way to attain Enlightenment then again some sects in Buddhism accept karma as a factor.
Not knowing (gnosis) what your karma was in your previous life and how it affects your current life to attain Enlightenment makes you wonder about the illusory nature of karma or Buddhism itself.

What's the view Buddhism has on your own chances to obtain Enlightenment? 
Is it because Enlightenment is just like truth and there are different degrees of Enlightenment? Is it because Enlightenment is like a path or direction you take in existence like a boat that heads west but the wind (karma) sometimes prevents you from moving forwards? Is it because Enlightenment is just like a riddle the Buddha plays to tell you about that characteristic of perception that makes you realize something that was always there but you were unaware of, or perhaps Enlightenment is the ultimate version of that? Or perhaps there is no Enlightenment and it's just the pursuit of it that gives us purpose in life and therefore less suffering (as long as we take the middle way of course...)?


  "There is no spoon" The Matrix
Enlightenment comes as a natural result of the meditation practise. When you practise meditation with proper effort you'll realize very quickly that this is path of freedom from suffering. So with experience a person realizes the benefits of meditation and that realization can lead the person to get involved with meditation more deeply. 

It is "not" possible for a person to not become enlightened If s/he is able to get rid of his physical and mental addictions, learns to practise mindfulness correctly and practises mindfulness and meditation for long periods of time. But modern life's requirements, the person's attachment to wrong ideas/beliefs and the possible mental or physical problems limits a person's conditions to do what is necessary in the path of freedom from suffering. So the chances to have success in the path is not just about freewill or karma. It's about both of them.

You don't need to be a Buddhist or subscribe to any religion or tradition to have benefits from spirituality. Also Buddhism really leads people to become Non-Buddhists If one follows Buddhism correctly. Just like Thich Nhat Hanh said "Buddha is made of non-Buddha elements". 

If you want to start to walk in the path, this map can be helpful to you: https://www.youtube.com/watch?v=ErN4a5qvxok