XnView shows a black or dark gray background but using the Extract Channel command to extract the alpha channel extracts it correctly. Apparently the black background is the norm for this, as it was the same with a .png that I created. Some applications use a gray & white checkerboard for transparency. Perhaps Canvas is recognizing the transparency. If it has some kind of channel manipulation commands, check to be sure.

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken