Tk's widget demo has precisely what you want, in "The canvas item types" demo. It also lets you see the code.

Basically, you want to use Tk::Canvas' createWindow command to display a child widget in the canvas:

use Tk;

my $mw = new Tk::MainWindow;
my $c = $mw->Canvas(-width => 300, -height => 100)->pack;
my $text = $c->createText(20, 20, -text => 'A text item');

my $but  = $c->Button(-text => 'Push me!',
              -command => sub {
            colour_text('red');
            $mw->after(500, [\&colour_text => 'black']);
              },
             );
my $but_i = $c->createWindow(70, 50, -window => $but);

MainLoop;

sub colour_text {
  my $colour = shift;
  $c->itemconfigure($text, -fill => $colour);
}
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