Indian citizen having layover in Shanghai for 21 hours.

Shaveta, you are perfectly covered by 24 hours visa free transit, so you really don't have to worry about possible delays of your flights and you don't need any kind of visa. I will explain why... 24 hours visa free transit takes in consideration ONLY your scheduled arrivals and departures, so in case that your plane is late, let's say 10 hours, you will be perfectly legal until the very departure of your plane to Canada. So, you can fly with absolute peace of mind.

One more detail... You would probably want to exit the airport. In this case you will apply for 24 hours free entry permit upon your arrival in Shanghai. You should have your flight tickets and your accommodation booking in hard copy and your chances to be allowed to exit the airport are really very good.

Thank you for your reply! That was really helpful.
I would like to know the procedure to get 24 hours free entry permit at the Shanghai Pudong international airport.

Also, It would be a great help if you let me know the charges to get the 24 hours free entry permit at the Shanghai pudong international airport.

In addition to this, can u please suggest me how much Chinese currency I should carry (for 3 adults) for some sightseeing and meals.

Thank you!

The procedure is straightforward and outlined on this site. There is no charge for the temporary entry permit. How much currency depends on what you want to do and eat.