Some points accept the cards and some don't. It's not a federal agreement on either side but agreement between states and provinces, so the rules vary across the country.
Easier to just get a passport, the hardest part is the little picture ;-) Should something happen and you needed to fly back home, you won't be able to without a passport. I don't think you can cross anywhere with a birth certificate any more. Certainly not WA/BC. I've never found customs to be a problem either way as long as you are cooperative and follow the rules....and I cross multiple times each year.