Canopus is a star.
In the canonical Star Trek universe, Canopus and Alpha Carinae were depicted as two distinct stars, with their own solar systems. This was contrary to the real word universe, in which Canopus and Alpha Carinae are the names for the same star, which is a white supergiant about three hundred light years away..
According to Star Trek: Star Charts (p. 65) and the Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), the Canopus (Alpha Carinae) system was located in the Beta Quadrant. The primary was a F-class star.
For Star Trek: First Contact, Alex Jaeger created a ship size comparison chart for Industrial Light & Magic. On this chart, one of the names considered for the Norway-class starship was the USS Canopus.