Though based on the same principles, laser cannons are more powerful than blasters. Laser cannons were originally used on starships to blast debris, such as asteroids, out of their way. These cannons were incredibly destructive, but did not target very accurately.
Eventually, pirates adapted this technology to their ships, increasing their accuracy, so they could be effectivley used in raids. To combat this, companies started to develop proper laser weaponary, making it more accurate while still retaining its destructiveness, for defense against pirates. The military quickly picked up this weaponary. Most starfighters and civilian ships will carry at least one cannon, and large captial ships have many. The technology was refined futher to Turbolasers, but these are too big for many small ships to carry.