Oral herpes or canker sore, what's the difference?

Very different. Aphthous ulcers (cankers) are on the gums or tongue, different spots on different days. Herpes will come on the same place on the lip, usually after a tingling (prodrome). Treatment ; symptoms are very different.
See. http://voices.yahoo.com/canker-sores-vs-cold-sores-whats-difference-2270211.html or http://www.Uhs.Umich.Edu/coldcankersores.