In the US, corn flour means finely ground cornmeal. Polenta is commonly used to describe cornmeal porridge but may also be used to mean plain cornmeal. However, unless whatever you're adding it to is allowed to boil, the result will taste starchy. As usual, give the recipe a trial run with the substitute some time when it doesn't need to be perfect. Corn syrup is common in the US but not always elsewhere.
Corn syrup comes in two flavors - dark and light.
Light corn syrup is just sweet, dark has a mild molasses flavor. A common US brand is Karo. The taste is mostly sweet, although there is a slight acidic, metallic component. Lyle's is a common brand. The New Zealand brand name is Chelsea.