I've never had a problem going north into Canada, but returning to the USA can be a bit of an ordeal at times and it can be quite quizzical.
Mrs. and I got searched coming back during the 1990's and all we had was a twelve pack of Vancouver Island Brewery's Scottish Cream Ale which the Customs jerks tried to confiscate at first until I demanded a receipt and when they got nasty I asked for a phone so I could make my complaint directly to Deputy Commissioner Lapham. Then they decided to give it back and let us go. I never mentioned that the only reason I knew Lapham's name was that I'd read it in the paper that morning.
Then, in 2001 (before 9/11) I was returning and the guy asked me if I had any firearms and I went down the list of what I had in the trunk and the guy looks at me and says, "Beat it, smartass!" and waves me through.
I doubt they'd do the same thing now, but it was kind of odd/funny at the time.