Handling arduino output current
As others have said, an Arduino pin can't handle 12V, and can't handle anywhere near 10A of current directly. A digital pin on an Arduino is limited to 20mA, or 1/500 as much current as you need, at 5V, which is less than half the voltage you need.

If you try to connect 12V to a pin on an Arduino pin you will almost certainly destroy that pin, and may destroy the entire Arduino. If you try to source or sink even 1/100 of the current you are talking about through an Arduino pin, even at 5V, you will also probably destroy that pin and possibly the entire Arduino.

This sounds like a good application for a power MOSFET transistor. With that much current you'll need to put a heatsink on the transistor.

Here's one that would work:

https://www.sparkfun.com/products/10213

You'd use a logic pin from the Arduino to control the gate on the transistor, and the transistor would switch 12V at high current with very little resistance.

If the actuator is inductive, you'll need to protect the transistor with a suitably large "flyback diode" to protect it from the reverse current (or "back EMF") you get from an inductor when you remove power from it: 

https://en.wikipedia.org/wiki/Flyback_diode