I found that going into Canada with a firearm is going to depend on the agent you get by the luck of the draw.
I went into BC on a bear hunt, at the drive up window I declared that I had a rifle with me. The instructed me to pull into a inspection area and wait for a agent. The agent showed up and I handed him my filled out paper work, he too it and me inside and had me wait in a small room, he came back in and asked where the rifle was located in my truck. I told him that it was behind the seat, he left and the wait began. Over a hour later he came back and took me to their front desk where he had a form that he had filled out using my information that I had given him. Evidently he didn't like the form that I had printed off of my computer that looked exactly like the one that he now had in his hand writing. He then went on lecturing me that my rifle should be outside of the passenger compartment of my truck and not easily accessible to me. I mentioned that I had to stop my truck and get out to even think about getting to the rifle. He then took me back into the room to wait a while longer. After a full 2 1/2 hours I was brought into their main desk where I paid the fee and was free to go.
When I got to the hunting lodge I found that they had gone completely through my two bags that I had packed for the 23 mile horseback trip for my hunt. It looked like they had just dumped everything out and then shoved it back in. I had to repack everything.
On my return trip the US Customs agent asked me the usual questions. He asked about my rifle and if it was the same one that was listed on my 4457, I said that it was and that was as far as it went. I then had to fill out a couple of forms to bring my bear back into the US, in total on the US side it took me about 15 minutes and I was on my way.