when my friend's and i crossed the detriot-winsor border on our trip to canada last summer, we had our *car* FULLY searched. they even went as far as unwrapping the sleeping bags and went through each and every article of clothing in our luggage. during the whole search we just stood next to the car... it took about 20 minutes for them to complete the search (i thought it was very amusing that the "do-good-sissy" canadian image i hold of them was supported since they put every thing back where it was before... NEATER than it was before lmao). the funny thing is they never actually searched *us*... not even the large envelope-portfolio thing i was holding that had my passport and shit in it (it could've easily fit a oz and some x tabs ). i DID notice a customs officer with a dog... i'm assuming it was a drug and/or bomb sniffing dog. but the dog wasn't even close to where the customs parking lot was, it was a few hundred yards away from our car.
basically i'd say that if you want to bring over any goodies, you better mask the shit out of the smell (i'm pretty sure that even though the dog was far away and virtually unnoticable, it could probably sniff out skunk from very far away... if i HAD some weed on me, the dog probably would have had a fit)

summarizing, canadian customs will do an EXTREMELY extensive visual search of your car and whatever is in it, but probably won't search your person (they didn't even touch us). you could easily get weed past THEM, even if you have a sack in your back-pocket. but there's always that obscure dog..... dunno if you'd fool his snout.... only one way to find out really (i sure as hell wouldn't even attempt).

and as far as u.s. customs goes..... just don't declare the cuban cigar you bought over the border >_>