https://github.com/katzer/cordova-plugin-email-composer/blob/cab303d/README.md

var img_data = $scope.canvas.toDataURL("image/png"); // also tried "image/jpeg"
var options = { attachments: [ img_data ],
      subject: 'Enjoy!',
      body: 'See',
      isHtml: true};
$cordovaEmailComposer.open(options);