no, not even if over 18 in some states.
see link below
Termination of parental rights does not terminate one's child support obligation.
by paying it until it's paid off.
because the custodial parent passed away,
I suggest you consult with the other parent and an attorney on this. However, keep in mind that terminating parental rights does not terminate one's support obligation.
Make an official request with child support enforcement. see links
You can't terminate your obligation to support your child. That type of order must be decided by a court and only when the child is being legally adopted such that another parent will be responsible for the support of the child.
Age 19.
I'm not familiar with Canadian law, but moving the child out of state in the US would not terminate support.
Yes, until/unless the child is adopted. see links
Termination of parental rights often does not terminate child support obligations. All it does is terminate the right to visit your child and have any say-so in their lives.
Relinquishing one's parental rights does not terminate one's child support obligation.
Yes, it can. There's no magic number at which it becomes absolutely illegal for a court to terminate a child support agreement.