To clarify, foriegn pilots operating foriegn aircraft into the US only need to meet ICAO standards and the requirements of their home country, they do not need US licenses.

Also about canadian licenses, I think senior skipper is correct...you need a US license to fly a US airplane. But a US private pilot can fly a US plane into Canada and vice versa. But the conversion process between canadian and US licenses is very easy...there is a custom written test covering only regulatory differences, and no checkride is required for ANY license conversion (unlike ICAO).