If this is a single ticket and you only really have 3h layover in CAN you will not be making a transit without visa. You will simply have a international to international connection in CAN. When landing at CAN from JFK, follow the signs for transit/connecting flights, you will go through some sort of document check (not immigration) and get a stamp on your onward boarding pass and then you will find yourself in the departure area. No immigration, no security check. CAN is probably the easiest Chinese airport for international to international connections.