I'm not an immigration attorney, but I have made trips to Canada to find clients, and this is my understanding of the laws.

If you are a Canadian citizen or permanent resident, you do not need a visa to come to the United States as long as you will not actually be working and receiving payment from U.S. businesses or employers while in the U.S. For example, you can visit the U.S. to attend trade shows, meetings, conferences, etc. without a visa.

Here's a publication from the U.S. State Department that may help: http://travel.state.gov/content/dam/visas/BusinessVisa%20Purpose%20Listings%20March%202014%20flier.pdf