No, a Cajun spice blend usually contains more than just ground red pepper and garlic.  It often will have cayenne, onion powder, salt, and other spices – paprika isn't usually one of the ingredients.  Paprika will be a good substitute if you're searching for something to give your dish a little heat and flavor.  However, if you're looking for that Cajun flavor, you might need to find another blend of spices.