I have a bag of brewer's sugar, and underneath it it says (dextrose/invert/corn sugar).
Can I use this for priming? If so, ~3/4 a cup for 5 gallons?
Yes, that's perfect for priming! I weigh my sugar- I use 4 ounces per 5 gallons. I guess that's pretty close to 3/4 cup, I think.
Yeah, what Yooper said.
If you were feeling more adventurous you could check out the priming sugar calculator on the www.kotmf.com website...http://www.kotmf.com/tools/prime.php?PHPSESSID=7a8fb32b6cf78ae451ae02a5188a6c be
...which lets you work out how much sugar you'd need to get a style-specific level of carbonation.