@{
var canonicalUrl= String.Empty;

if(umbraco.library.RequestServerVariables("HTTP_HOST").ToLower().StartsWith("www")) {
  canonicalUrl = string.Concat("http://", umbraco.library.RequestServerVariables("HTTP_HOST"), CurrentPage.GetPropertyValue("umbracoUrlAlias"));
} else {
  canonicalUrl = string.Concat("http://www.", umbraco.library.RequestServerVariables("HTTP_HOST"), CurrentPage.GetPropertyValue("umbracoUrlAlias"));
}
<link rel="canonical" href="@canonicalUrl" />
}

@using umbraco
@using System

@{ var canonicalUrl= String.Empty; }
@if(umbraco.library.RequestServerVariables("HTTP_HOST").ToLower().StartsWith("www")) {
    canonicalUrl = string.Concat("http://", umbraco.library.RequestServerVariables("HTTP_HOST"), Model.Url);
} else {
canonicalUrl = string.Concat("http://www.",   umbraco.library.RequestServerVariables("HTTP_HOST"), Model.Url); }
<link rel="canonical" href="@canonicalUrl" />

@using umbraco
@using System
@{var canonicalUrl= String.Empty;}
@if(umbraco.library.RequestServerVariables ("HTTP_HOST").ToLower().StartsWith("www")) {
canonicalUrl = string.Concat("http://",  umbraco.library.RequestServerVariables("HTTP_HOST"), Model.Url);
} else {
canonicalUrl = string.Concat("http://www.",  umbraco.library.RequestServerVariables("HTTP_HOST"), Model.Url);
}
<link rel="canonical" href="@canonicalUrl"  />

@using umbraco
@using System
@* empty out the string *@
@{var canonicalUrl= String.Empty;}
@* check if  the requested URL starts with www. *@
@if(umbraco.library.RequestServerVariables("HTTP_HOST").ToLower().StartsWith("www"))  {
@* adds http:// to the beginning *@
canonicalUrl = string.Concat("http://", umbraco.library.RequestServerVariables ("HTTP_HOST"), Model.Url);
@* strips out the www. from the URL *@
canonicalUrl = umbraco.library.Replace(canonicalUrl,  "www.", "");
} else {
@* if they did not use the www prefix, we still have to add http:// to the URL *@
canonicalUrl = string.Concat("http://", umbraco.library.RequestServerVariables("HTTP_HOST"), Model.Url);
}
<!--  output the canonical URL -->
<link rel="canonical" href="@canonicalUrl"  />