For us going to Canada normally means travelling to Vancouver, BC for the day. Back in the day this was a fun outing.
Since 9/11 things have changed. Our usual experience now is that during the border crossing experience on I-5 at Sumas heading north the Canadian agents are generally professional and cordial, while heading south the American agents can be arrogant and even downright surly.
As stated previously have your passports ready, hand them to the agent, answer his questions correctly without imbellishments and hopefully you will be on your quickly, especially when heading back into the states. One time I did not hand our passports to the U.S. agent quickly enough and that did not make his day. He was not happy. I was relieved when he finally waved me "on" rather than waving me "over".