Or look for a Marumi one. They're made under licence from Canon, are a bit cheaper, and (to my mind at least) seem to be made from slightly better quality plastic.
Make sure you get the right one. Lots of lenses have 77mm front elements but the size and shape of the hood varies. For a Canon EF 70-200mm f/2.8 L you need the ET-83 II; for the 70-200mm f/2.8 L IS you need the ET-86. (The IS version of the lens is actually 3mm fatter at the business end.)
But didn't your lens come with a hood? It should have.