I would not rely on a Taser for defense situation on any extended outdoor trip. They are battery operated after all. Tasers available to consumers do not work as well on large animals as they do on humans. I recall seeing a video where an experimental (much stronger ) Taser was used on a bull with some success, but this is nothing available for the hiker.
The Taser is designed to immobilize the subject for 5 seconds for law enforcement applications giving enough time to handcuff the suspect. The civilian model immobilizes the subject for 30 seconds giving the user time to escape. Even if that did work on a bear, I don't think 30 seconds is enough time to get far enough away from an angry bear no matter how fast you run. The range of the probes is 15 feet for civilians.
I think the only alternative to carrying a firearm, if you feel you need the protection, is a can of bear spray. You should train on deploying the spray quickly and with confidence.
Most important, more so than any equipment or weapons you can carry, is knowing your area, knowing the signs of predators in the area, knowing their behavior, having a plan, taking preventative measures (like proper food storage) and staying aware of your surroundings at all times.