I'm Australian. Just do your homework and make sure the farm is reputable/honest. I know a Canadian guy that had to take some of his personal experiences to local newspapers to get all the money he was owed. They were trying to force him to stay.
Migrant workers are commonly exploited, and there are a lot of shitty farms. But if you play it smart you should be fine. Maybe just go on a reccommendation from another backpacker?