Whoa.
Canned fruit is supposed to be heated to a certain temperature. It ought to kill any eggs or maggots. If I ever got live bugs out of canned fruit, I'd contact the manufacturer with the batch number off the can and I wouldn't eat that brand again. Being the troublemaker I am, I'd probably also notify the market.
If canned food isn't heated properly, you could get a lot worse than fruit flies.