What exactly are you trying to copy from the canvas, a screenshot of it's contents?

I couldn't find the clipboardClear or clipboardAppend methods in perldoc Tk::Canvas, so I think you are thinking about this wrong. Maybe you think it is like Gimp, where you can select rectangular regions and save them as graphics to a clipcoard?

The only thing I've seen used is to capture the entire canvas as postscript, or use Win::Photo to capture as a jpg, or png,etc.

The only one which allows you to select coordinates is postscript, and you might be able to select a region, with a mouse drag, and substitute the values into something like the following code:

$mw->Button(
    -text    => "Save PS",
    -command => [sub {
         $canv->update;
         my @capture=();
         my ($x0,$y0,$x1,$y1)=$canv->bbox('all');
         @capture=('-x'=>$x0,'-y'=>$y0,-height=>$y1-$y0,-width=>$x1-$x
+0);
         $canv->postscript(-colormode=>'color',
                               -file=>$0.'.ps',
                               -rotate=>0,
                               -width=>2400,
                               -height=>3400,
                               @capture);

                      }
  ]  )->pack;
[download]

You need to show us some code of what you are actually trying, because we are just guessing at what you want.