This button will display the Page in the 3D Viewport
This button will clear the Page from the 3D Viewport.
Changes the scale of the Page in the 3D Viewport
Changes the opacity of the Page in the 3D Viewport
Flip the image in the viewport in the x direction.
Flip the viewport in the viewport in the y direction.
Resizes the Page so that it is at the same exact dimensions of the 3D Viewport.
Note that this is not the size of the render region, it is the size of the actual 3D window itself.
When you have a Canvas in Full Viewport mode then you can use any of the Canvas Tools directly in the 3D Viewport itself. You can draw shapes, move, select, align etc... directly in the 3D View over the top of your models.
This allows you to draw shapes onto your objects and then Project them down directly onto the materials, or use use the "Paint Brush Standard" tool to paint the canvas onto your objects.
Move the Page around in the 3D View.
Note: If you have Full Viewport enabled then this should not be used.