I've never thought using a canister as a reactor would be beneficial. The point of a reactor is to allow flow up and THROUGH the media. They have clear canisters to be able to monitor the media and usually come with ball valves to control the amount of flow to produce the required amount that best suits the media.
for example, clumps very easily, and requires a "slow boil" for it to be effective. It is also soft, and if the flow is too strong, will wear away by colliding into itself and fine particles will enter the tank. If the flow is not strong enough, then it will clump up and the water will go around it, instead of through it, completely defeating the purpose of the media.
Carbon is best off with different flow as well, as it's even softer, and need not tumble at all, which is why if you have room for a separate reactor, you're best off.