my $platform_independent_path =
      canonpath "../data/somepath/somedata.txt";

my $directory_separator =
      canonpath "/";
[download]

Erm. No.

All canonpath does is clear up a directory in to a canonical for for a specific platform - it's not platform independent in any way.

For example running your code on a Mac OS 9 box would set $directory_separator to "/" when it would more accurately be ":".

As rinceWind points out the idea of a single separator isn't valid on some platforms in any case.