That menu entry (File->Canvas-> New Canvas) has been never active. Maybe we should think on re-work some of the menu entries.
To create a new document with a root canvas in it just press the (New…) button in the toolbox.
You can create in-line canvases by encapsulating a group of selected layers. It will create a Paste Canvas Layer that acts like a folder of layers. In line canvases can be exported (by right clicking the canvas parameter of the Paste canvas Layer and select a name). Then, the exported canvases can be referenced by the canvas parameter of the Paste Canvas Layer that can be animated between different exported canvases.
-G