I'm a little unclear about what you want exactly. It does appear you are missing -scrollregion. Does this small example do what you want?

#!/usr/bin/perl

# http://perlmonks.org/?node_id=1137318

use Tk;
use strict;
use warnings;

my $mw = MainWindow->new;

my $canvas = $mw->Scrolled(Canvas => -scrollbars => 'osoe',
  -width => 1000, -height => 400,
  -scrollregion => [0, 0, 1000, 400],
  -bg => 'green',
  )->pack;

MainLoop;
[download]