Here's an interesting article that shows behavioral and physical traits in a dog may predict his or her success as a service dog. Something to pay attention to when selecting your next dog! Front paw preference (right or left), eye preference (left or right is the more dominant one) and hair swirls (clockwise vs counter-clockwise) could be key in pre-determining the success of your canine partner as a your service dog. According the to the results of her study off 115 guide dogs, it could be key.
According to the article, the perfect candidate for Guide Dog school would be right-pawed, left-eyed with an anti-clockwise whorl.
Assuming the experimenter is correct about the use of dogs on the right side of the handler, left-handled handlers may be better to choose a right-eyed dog and train them to work off their right (as in heel on the right), which in left hand-drive countries, would be safer anyway since the dog would be away from traffic.