flatten image to transparent

[kumado]

Hello all,

   I am new to the forum.
I did a couple searches, been over Google a bit but ....

   If I can explain this: ( I am sure I might not use the "proper" term somewhere, please excuse me )

    I have a png image with a transparent background.
    If I re-size the canvas, the only method I know to make the new image include the
expanded canvas is to Image -> Flatten Image.
   This removes the transparent background and replaces it with the present background color from the tool bar.
   The same type of thing happens to me with text. In order to have the text as part of the image,
I have to go to Image -> Flatten Image. Once again it removes the current transparent background
and replaces with the present background color from the tool bar.

    My question(s) is/are then:

    Is there a way to make the image not loose the transparent background, ie
use something other than Flatten Image
    or
    Is there a way to set the background selected color on the tool bar to transparent?

Thanks so much for your time,

kumado