I've packed lunches before for Alaskan ports, I don't know about Vancouver. Just bring along some zip lock bags to store your food. Maybe Princess will pack box lunches, but I don't know - I'm sure you get a response from those in the know :o)
We ordered sandwiches from room service the night before we reached port and kept then in the fridge over night. The we packed them in a soft sided collapsible cooler when we went ashore and enjoyed a picnic lunch when we got hungry. Since Alaska is USA, there was no problem there, but there might be in Vancouver. Someone else might know about that.