This is not about Canadian law, but about the logistics. I suppose that if OP is traveling with a day pack which he can sling over his shoulder and simply not return to the ship, it does not matter what the cruise line things, says or does. But, if he has luggage which needs to be physically delivered to the disembarkation point and delivered to Customs for pickup at Halifax, that needs to be arranged in advance if it is available. If it is not available, OP has the option of simply walking away from the ship and not returning and figuring out how to reclaim his luggage at some point in the future.
As a Canadian citizen he may present himself without even a passport and he will eventually be admitted. The question is not whether he will spend his life on some pier in limbo, but how simple and pleasant all of this is.
Hence, my advice to simply call the cruise line. If it is not available, it is not as though the Captain will have OP held in the brig at Halifax. People call all day and every day with questions.