'polyamory' is illegal in Canada as it is seen as "polygamy." The difference is religious in nature... in polygamy men take on young wives to add to their households because they believe it is their right... the women are not consulted and are often very young.
there is a thread on the court case going on etc...
From what I know the word "polyamory" has been around since the early 90's... when I came out about 15 years ago it was just "non-monogamy" as far as I knew. I didn't know the word poly until 4 years ago.