There's a lot of information and links regarding the laws in Canada stemming from the BC Reference Case on Polygamy and Group Marriages
which wrapped up with a decision this fall. Check the late part of the thread with some articles regarding the legal opinions around the decision.
There was a further custody case in Australia I think where the judge simply threw out any evidence about a poly relationship as irrelevant.
You'll need to get your own legal opinion on what you can do, and what your risks with custody or family issues, and make your own decision. However the gist of the decision from the reference case is that poly relationships themselves are legal...just the ceremony really that causes the problem. And if you're not doing anything illegal, then the teachers and neighbors should be minding their own business instead of yours.
Of course, what should be and what is, isn't always similar...especially in Halifax.