I've been searched and non-searched (never bring Aussie's to sasquatch!) and being searched in the worst thing. Even though I never ever bring anything I always feel like they're going to find some secret drug compartment that I never knew existed. I couldn't imagine actually trying to smuggle something across the border. I'd throw up! And that would just be super obvious.
I've never been searched, and the last time I drove home from the US I had more than a case of wine in the trunk. I declared all of it, and they actually went pretty easy on me as far as duty (they way under-assessed me). If you don't bring any illegal substances over the border and you're honest, you probably won't be hassled too much if at all. I'm across the border often enough between flights and driving that they usually just wave me through, more or less (both directions)
Red flags for the border seem to be (from past experiences / friends): 1) if you appear to be dishonest / nervous / jittery 2) if you do something to make them think you might have drugs (wearing pro-legalization t-shirts for example) 3) if you're in a rented vehicle or the registered owner of the vehicle is not present (you borrowed your parents' car)
Oh, and if you're over 18 but under 21, DO NOT BRING ALCOHOL ACROSS THE BORDER. Yes, you're legal age here in AB, but you're not in WA, and you don't want that hassle. Make friends with someone at the festival instead.