From experience.....
The cruise line should be contacted. Then once clearance is awarded and you are onoard, the Purser's office should be consulted for disembarking instructions. There is a system in place to clear disembarking passengers.
Do note that you will be instructed to notify your cabin steward. You will pay all gratuities for the entire cruise. You must handle all of your luggage from cabin to pier. Your boarding pass will be turned over to security and you cannot reboard even to grab all of your luggage.
And, finally, we have missed docking twice in Halifax due to fog and high seas. The sealane into the harbour is narrow. Just so you know that any docking is not guaranteed.