回複：買房買來的煩惱，請指教

1) From my experience (in US, might not be true in Canada), lawsuit with HOA is a very bad idea. Cost tons of the money and HOA normally wins.
2) I think your best chance is to persuade neighbors. Is this deck for your use only? Can you open it to other neighbors to use as well? Is it possible for neighbors to build their own decks and connect them together to be a common area? This way, at least your kid can have a safe place to play. I would suggest NOT arguing that you had the right to build the deck; but arguing it is a safety concern and try to make it beneficial to your neighbors.

Good luck.