Throughout the game i have collected a bunch or rare candies. I have also finished Ev training all my poks. Such i continue training my poks. by battle or use the rare candies i have found throughout the game?

That's called unnecessary level grinding. Since you've EV trained your pokemon I wouldn't bother to train them more since you might mess up their EV sets. Unless you maxed out whatever stat you trained in.

To answer your question, you really don't need to.

If your Pokemon have the maximum total 510 EVs, they will not gain any more EVs and therefore, any way of leveling up (battling, rare candies, etc.) is fine. To make sure that they have the maximum 510 EVs, go to the lady in Sunyshore Market if you haven't already. She will give any fully EV'd Pokemon the Effort Ribbon.