The Gnome2::Canvas is pretty basic. There are no such thing as tags( like in Tk). In Tk you can say something like "find all items with tag equal to whatever". In Gnome2::Canvas, you can make your own like

my @lines;
my $line2= Gnome2::Canvas::Item->new ($root,
                'Gnome2::Canvas::Line',  
                points => $points,                      
                fill_color => "red",
                width_units => 8.0,
                join_style => 'miter',
                );
$line2->{'tag'} = 'red', # maybe an array_ref for multiple tags?
push @lines, $line2; 

foreach my $line (@lines){ 
    if( $line->{'tag'} eq 'red' ){print "$line is red\n"} 
  }
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use Data::Dumper;
print Dumper($canvas->root, $canvas),$/;
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