Finding out if a marriage is legal.

Our father went to China a few years ago and got married. He recently passed away and left no will and we are unsure how to find out of their marriage was legal. Canada immigratin denied her to come to Canada and when he appealed it, it was all denied. Our two main questions are: Can you get married without all the documentation, specifically anything saying he was in fact divorced?
And if there is a way to get the information quickly if we can not find the forms among his documents?