I have a flight to canada via Shanghai pudong airport with 4 hour layover.

The correct produres are Joint Inspection & Quarantine & Immigration - International Luggage Claim - Transfer Hall - Go to International Concourse on 3F. Thus you need to go through the immigration.
You don't need to apply for the visa. You can enjoy 24 hours visa free policy because your stopover is just 4 hours. In addition, your have enough time to make this connection. Generally speaking, the China Eastern Flight won't be delayed unless the bad weather conditon. Don't worry. Just take it easy!