I grew up on canned fruit, mainly pineapple. It was in juice, so I thought of it. I found out the difference later on in life. I always stayed away from fruit in light syrup.
Any food swimming in juice or "light syrup" isn't good for you. Furthermore, most canned fruit is peeled, meaning you're being robbed of a valuable source of fiber. Frozen fruit is a little trickier. Freezing preserves the fruit itself, but some manufacturers add sugar during the freezing process to preserve color and taste. Most fruits can be found in the frozen food section.
You have to read the ingredients list! You want it to say fruit, water—and that's it. Nothing more.