I wouldn't consider the Slickback to be a Canopy.
Canopy is front or rear half.
The Slickback was the simplest and likely cheapest way to add a VT option to the Barracuda FB.
To me it's simply a VT in the same way as GM did them for a while with perimeter moldings.
Look at a '69 Camaro or early Monte Carlo for example.
Calling it a Slickback was marketing hype - more exciting to the execs than "vinyl top".