How do the similar cultural and economic environment of the united states and canada help to keep people and goods passing easily from one country to the other?

Answer 1

The U.S. and Canada trust each other. However, in the last two years, Canada has required a passport from everyone, including Americans, coming into the country. The U.S. has similar requirements.

http://gocanada.about.com/od/canadatraveloverview/qt/uscitizenborder.htm