Try this.

sub AlignAll{
    foreach my $i (0 .. 3) {
        my( $x1, $y1, $x2, $y2 ) = $sc[$i]->bbox('rect');
        my $location =int(($x1+$x2)/2);

        ## The location minus half the width of the window 
        ## Over the scaled width of the drawing
        my $abs = ( $location - 200 ) / ( $initial_width * $scale );
        $sc[$i]->xviewMoveto( $abs );
    }
}
[download]

With the addition of -confine => 0 when you create your canvases,

    $sc[$i] = $tile[$i]->Scrolled('Canvas',
        -confine => 0,
        -scrollbars => 'os',
        -scrollregion => [0, 0, $initial_width, 125],
        -width => 400,
        -height => 125,
        -background => randColor()
    )->pack(qw/-fill both -side top -expand 1/);
[download]

it aligns and centres the boxes at all scales from when the entire arrow is just a blob through to the box being bigger than the window.