I suppose it depends how you define 'canon.' Sherlock Holmes fans use it to mean novels written by Conan Doyle. The Bible means the 4 gospels of Matthew, Mark, Luke and John.
If you apply the same sort of criteria to DW, I would argue that the likes of books, radio dramas, DW unbound and the Cushing movies fall outside the definition of canon, no matter how influential they have proven to be or how well they fit in within the continuity of the series.
But like Christopher
says, it's all fantasy anyway, so does it really matter? Besides, IMHO, some 'non-canon' stuff from any series or franchise can be more entertaining than the canon stuff. Many of the Treklit novels for example.