Polylang Canonical Tags with Yoast's API

canonical.php

<?php

/**
This is used on a site where blog posts are in each english region, to avoid content duplication this method generates
the canonical for the main English site language 
**/

function is_blog_page () {
  global  $post;
  $posttype = get_post_type($post );
  return ( ((is_archive()) || (is_author()) || (is_category()) || (is_home()) || (is_single()) || (is_tag())) && ( $posttype == 'post')  ) ? true : false ;
}

add_filter( 'wpseo_canonical', 'blog_canonical_generator' );

/**
 * Get the EN transation for english speaking blog posts, to avoid content duplication across english languages.
 * @param  string url - Yoast's canonical url for the queried object
 * @return string - EN url or default for non english speaking
 */
function blog_canonical_generator($url) {

  $currentLanguage = pll_current_language();

  $englishSlugs = array('en-nz', 'en-gb', 'en-us', 'en-ca', 'en-au');

  if ( is_home() ) {

    $post = pll_get_post( get_option( 'page_for_posts' ), 'en' );

  } else if ( is_blog_page() ) {

    $post = pll_get_post( get_queried_object_id(), 'en' );

  }

  if ( isset($post) && in_array($currentLanguage, $englishSlugs) ) {

    return get_permalink($post);

  }

  return $url;

}