What is the difference between Kafka Channel and Kafka Broker?
What is a Kafka Broker?
Kafka is a distributed streaming platform. It is run as a cluster on one or more nodes, and each node in the cluster is called a Kafka Broker.
What is a Kafka Channel?
A Kafka Channel is a type of Flume Channel. Flume is:

Apache Flume is a distributed, reliable, and available system for efficiently collecting, aggregating and moving large amounts of log data from many different sources to a centralized data store.
The use of Apache Flume is not only restricted to log data aggregation. Since data sources are customizable, Flume can be used to transport massive quantities of event data including but not limited to network traffic data, social-media-generated data, email messages and pretty much any data source possible.

A Channel is:

Channels are the repositories where the events are staged on a agent.

So hopefully, it is now clear that a Kafka Channel, is a Flume Channel that uses Kafka.