Flight from Cambodia to Tokyo, layover in Shanghai

My sister and I (both US citizens) plan to get a flight from cambodia to Tokyo with a 12 hour layover in shanghai. Our home airport, (the one we leave from to go to Cambodia and the one we leave to after Tokyo) is Vancouver. We have all those flights purchased when we land in Shanghai for our layover. Will we still be able to leave the airport in Shanghai for a few hours of sightseeing?