Sunflower oil for seasoning cast iron
Absolutely!

You can use most any oil on hand. Sunflower oil is a little pricier than others, but works well and has a neutral flavor. I use it occasionally for maintenance/cleaning on my Griswald #10.

It's not necessarily tolerance to heat that you're looking for in an oil, but oils that polymerize easily, which is (chemically) what you are doing when you season cast iron.

See also: What oil is best for seasoning a cast iron skillet?