If you do have a full 5 gallons to bottle, I have used 2/3 cup of corn sugar. I know a calculator would be more accurate, but it's pretty close. I've had no problems.
The priming sugar I bought just says priming sugar I got it from northern brewers it's a fine powder no other writing on label is it sucrose corn sugar or dextrose cane sugar I have no idea or does not matter ?
Dextrose IS corn sugar and is likely what Northern is including. I can't say for certain if it's any other type of sugar or mix but I feel pretty certain it's just simple, and inexpensive, dextrose.