How wide is North America from coast to coast?

That depends upon how you measure it. At its widest point from far western tip of the Alaska's Aleutian Islands to eastern Greenland, it's about 7,000 kilometers. Check this map.

http://www.google.com/imgres?imgurl=http://www.mapsofworld.com/north-america/maps/north-america-map.jpg&imgrefurl=http://www.mapsofworld.com/north-america/map-of-north-america.html&h=598&w=550&sz=115&tbnid=Z5TMBuL8lNUJ::&tbnh=135&tbnw=124&prev=/images%3Fq%3DNorth%2BAmerica%2Bmap&hl=en&usg=__w5S10niQKTrRFokVATI31RHRMFw=&sa=X&oi=image_result&resnum=4&ct=image&cd=1