They don't cavity-search, they just get the dog. And the dog will bite you to tell the officer you're carrying. Thats according to that tv show about the DEA.
Every time I cross, they search my vehicle. First time, they checked my trunk because I guess something in my camping gear triggered some warning for them. Every other time, they searched my whole vehicle.. Under the hood, the trunk, glovebox, seats, even removed my backseat.... That second time, I had *just* detailed the interior, and found a roach when I did!!!!! I'm so fucking lucky, you have no idea. I watch all those cop shows. Lucky find too, got me so stoned, and no idea how old it was. I freaked afterwards because it must have been there the first time I crossed.... but during, I was very calm, I knew there was nothing in my car. Being very calm is also alarming for them, almost as much as being shifty. The DEA agents mentioned that, when they were searching some truck and the driver was super cool about it. They ended up finding a huge amount after they tore the rig apart.. but on first pass (removing tires, etc) they couldn't find anything. I'm sure when I cross, something about that vehicle triggers their sensors because of all the residue from nitro salts or whatever, due to regularly transporting firearms and ammo to/from the range. I was questioned about some empty cases in my trunk for rifle ammo, almost interrogated about it. On one trip I saw a black triangle-shaped craft way above the highway, about 30 minutes from the border before I entered the USA... At first I thought it was some American craft or something, but it was hovering, so I thought it may have been a kite... Then I looked up again and it was gone. Made no sense because I kept glancing up at it and then it wasn't there anymore.. so now I think it was something else.
I'm so surprised they're bent on searching when I cross, I'm way more interested in what I could be bringing back! I've never been searched on my way back. I could have grabbed some tracer rounds, or other stuff... Lots of fun stuff available for guns that we don't have here. Anybody interested in tracers should know that rimfire tracers are apparently legal in Canada, but I've never seen them for sale anywhere. Center-fire tracers are prohibited. Not very useful in most situations because most ranges have a "dawn to dusk" type of rule on shooting.. Target shooting at night, you have to be on private property. Out in the Crown-Land, such as for hunting or sporting, your gun has to be locked up at dusk. Thats because some people duct-tape flashlights to their rifles and look for the deer-eyes at night, which is illegal hunting. I digress....
I wouldn't try to smuggle anything into the US. They have so many sensors now, not just X-Ray. One guy on DEA begged to be searched after the agent said the dog would bite, and he had it in his ass. Then again, cops often say things in hopes of people incriminating themselves.