Airplaneholic,
A green card allows you to be a permanent resident... You would still be Canadian. A green card is what you need in order to live and work freely in the USA as a Canadian citizen.
I am a US citizen, I DO NOT have a green card. My wife is a foreigner and she does have a green card.
If you want to work in the US, a green card is exactly what you need and you would still be Canadian.