Egg is a good treat for canary especially for nestling canaries. However, if used a lot for adults, it is going to be harmful as it will make them fat, influence their health and productivity. However, a little bit once a week would be a good choice.
Fruits are good for canaries, yet, you need to be aware of some toxic ones. Generally, keeping a variety of foods is integral for the canary to keep singing strongly, loudly, frequently and continuously.