You didn't specify what hardware you want to use so I'm free to choose any hardware that may fit your description.
If you use the Sparkfun Load Cell Amplifier you can connect more than 3 load cells to one Arduino and monitor them more or less simultaneously. Just use different pins for clock and data for every cell connected and use the linked library to access them.
The wires from the load cell to the amplifier have standard colors and the pins on the amplifier are labeled accordingly.
The wiring from the Arduino to the amplifiers depend on what you want to attach to the Arduino additionally. As you haven’t told us what your project is about we cannot suggest a solution other than using separate pins for every amplifier but that’s obvious.
Connect 3 load cells to a single arduino so it can read the data from the sensors and then send it to a server I’ll run ( raspberry pi ).
How do you plan to send that data to the Raspberry Pi? Serially? Ethernet? Wirelessly?
You can connect to any free GPIO pin on the Arduino. But which pin is free depends on the hardware you plan to attach.
The input I saw was based on connecting the arduino (in my case uno) via a cable to the raspberry pi.
I guess this means that you connect it by USB to the Raspberry Pi.
What do you mean by the term: “Hardware you plan to attach” ?
If you want to connect the Arduino by Ethernet to the Raspberry Pi you need additional hardware (Ethernet Shield in this case) and additional hardware has to be connected to the Arduino using pins which are not available for other stuff then.
In your case you can connect the load cells to pins D2 - D7 of your Arduino UNO.