Well as it stands, legally the ownership of the gun would be that of the parents till you reached the legal age of maturity, they can how ever allow you to use it, but legally they must be supervising you at all times during use.
I seems you have a grasping of how the details of airsoft are in Canada and I commend you for taking the time to read.
As for what fields will allow you to play, as it stands I believe that being able to play or not is up to the owner of the field. Good luck with your inquiry unfortunetly I am unable to offer much more information and hopefully someone else can aid.
"Its only a little bit on fire"