The system is being updated and the CP flight has to be taken off (which is why it is shown as cancelled) and then the new AC flight has to be uploaded.
Just to be on the safe side, why not just take the 6:30p instead since it's a A340? Even if it shows international J now, they could always change it to domestic J anytime. It will not be a purple elvis because that's a CP plane and since it is now in AC flight number.