Canthoplasty done twice with poor results. Is there an alternative surgery?

  The details here are a little obscure to me.  One reason is that one surgeon's canthoplasty technique may vary from another's.  Certainly, an oculofacial plastic surgeon should be able to give you the results that you are seeking and there are a number of excellently trained oculofacial physicians in your country.

Canthoplasty is not a magical procedure.  It sounds like your surgeon may not know what they are doing.  An experienced oculoplastic surgeons should have no trouble getting the lateral canthal angle set posteriorly enough to sit against the eye so there should be no gap.   It is very reasonable to seek other opinions.  Photographs of your actual eyelid would be very helpful to address your questions.  Consider reposting with photos to elicit better and more meaningful answers.