I think the canon is only useful in terms of telling you the stuff that has lasted but it's arbitrary- down to prevailing tastes and ideologies- trying to make a canon on anything on the last thirty years or so is almost impossible - the test of time can be very harsh. In the early twentieth century George Meredith was hugely popular but almost no-one reads him now. John Donne languished out of favour for centuries before being reclaimed by TS Eliot and others. DH Lawrence was once slap bang in the middle of the canon and is now slipping outside. And, of course, there are plenty of voices that got left outside of the canon - the work Virago did to reclaim female writing was phenomenal but it's shocking to think it had to be done to reclaim these writers from the shadows.
And, in the end, once you done enough of your own reading, you develop your own canon - your compass by which you navigate the choppy literary waters. And that is fine - you can't like everything, nor should you, but trying to claim something as better is a fool's errand because i don't think there can be a true objectivity - a book read at twenty is a different proposition at 40 - i do think it is useful to be aware of the canon for the cultural capital but equally important is to realise it is no more than a gateway.