Commanding a 12V DC motor with high power (~20A)
It might be fun to implement your own H bridge with external MOSFETS, such as the P channel FET that you linked to, plus N channel FETs for low-side with similar parameters. 

You would have to implement a lot of protection measures though with discrete components that it might be better to find and implement a circuit which external switches but based mainly on a H bridge controller IC. The controller IC will have push/pull or charge pump MOSFET gate drivers for hard and fast control of the external MOSFETs, meaning you will waste less heat, and some have the option for current sense resistor feedback for over-current protection and other nice features. 

Make sure you include clamping diodes to deal with back EMF.

Of course if you have little experience, it might be better to first make some simpler lower power H bridges first, and then work up to a nice big fully controlled high power one. 

You may also buy motor controllers (for quite a lot of money) and save yourself some time and issues with testing. You show Sparkfun as a website in your link, perhaps check out the products available at Pololu's website, there are some nice motor driver solutions there. 

You may also consider trying to change the motor you are using, to a 24V or 48V motor, to half or quarter the amount of current used for the same approximate 'power' output. Current is the killer, in terms of heat and nice explosions, so trying to reduce the amount of current to something less crazy would be something to look into for your project/design/thing.