2D World Environment / Glow:
To affect 2D/Canvas Nodes you have to set the WorldEnvironment mode to Canvas
.
Then in order to make a visible difference — in the Glow settings, set the Blend Mode to Additive
and then turn down Hdr Threshold
and/or Hdr Scale
values.

CanvasLayer Solution:
CanvasLayers (as indicated by their name) allow rendering on a specific drawing layer. By default CanvasLayer renders above the standard 2D scene and is thus also not affected by the WorldEnvironment glow effect.
This could be solved in two ways, first set the CanvasLayer's layer
below 0
(as vnmk8 has found out and answered), or alternatively in the WorldEnvironment, set the Canvas Max Layer
to 1
:
