Baggage checked from Beijing to Toronto (via Chicago) on United. Will I need to collect luggage in Chicago and re-check for final leg from Chicago to Toronto?
Yes you will have to collect and recheck baggage. You will go through US Customs and Border Protection too.
Step 1 : Arrive at O'Hare International Terminal 5
Step 2 : Proceed to Customs and Border Protection (CBP Processing Area - Immigration Inspection
Step 3 : Claim Baggage
Step 4 : Proceed to CBP Processing Area - Customs and Agriculture Inspections
Step 5 : Connecting Flights/Transfers
Here is a really neat visual guide