Web Forms :: Provide SiteMapDataSource From Code Behind C#

in my masterpage I have the following:

<asp:SiteMapDataSource
ID="MenuSiteMap"
runat="server"
ShowStartingNode="False"
SiteMapProvider="SpanishSiteMap"
/>

In My code behind I want to provide the SiteMapProvider instead of having it hard coded from the aspx page. What would the code look like to replace in thie case 'SpanishSiteMap' and have that come from code behind in c#? I thought something like this but i know this is way off. hopefully someone has a one liner code that will give provide some sleep. I've come closer to a working code. this is what i have... but get the error mentioned below.

MasterPage myMasterPage = (MasterPage) this.Master;
// do a find control on myMasterPage and find the siteMapDataSource
SiteMapDataSource mySiteMapDataSource = (SiteMapDataSource)myMasterPage.FindControl("MenuSiteMap");
// now u have the reference to the siteMapDataSource used in the master page how do I set the provider..
mySiteMapDataSource.Provider = "SpanishSiteMap";

Error: Cannot implicitly convert type 'string' to 'System.Web.SiteMapProvider'