Can I use sunflower oil to season my cast-iron pan? I know the oil needs to be able to tolerate high temperature and I'm not sure if this oil is fit for purpose.
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.