Set default MembershipProvider based on DropDownList in ASP.Net

I have two connecting string and two memebership default provider.

I just want to call the membership default provider when login page I select AD, then the page know how to connect to the ADmembershipprovider and when I select ACAD, then it’s will direct to the ACADmembershipprovider.

Please help. Thanks.

    <connectionStrings>
      <add name="ADConnectionString" connectionString="LDAP://ad.fullerton.edu/DC=ad,DC=fullerton,DC=edu" />
        <add name="ACADConnectionString" connectionString="LDAP://csufacad.fullerton.edu" />
        <add connectionString="Data Source=hhdsrv02;Initial Catalog=DBHUSR; Integrated Security=True" name="DBHUSRConnectionString" providerName="System.Data.SqlClient" />
    </connectionStrings>
    <system.web>
        <membership defaultProvider="MyADMembershipProvider">
        <providers>
            <clear />
          <add name="MyADMembershipProvider"
                    type="System.Web.Security.ActiveDirectoryMembershipProvider, System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"
                    connectionStringName="ADConnectionString"
                    attributeMapUsername="sAMAccountName" />

          <add name="MyADMembershipProvider"
                   type="System.Web.Security.ActiveDirectoryMembershipProvider, System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"
                   connectionStringName="ACADConnectionString"
                   attributeMapUsername="sAMAccountName" />
         </providers>
      </membership>     
    </system.web>

Here is my login page code

    <table>
        <tr>
            <td><p class="pad1"><u><asp:Label ID="Label2" runat="server" Text="Select Domain:"></asp:Label></u></p></td>   
            <td><p class="pad2"> <asp:DropDownList ID="DropDownList1" runat="server" DataSourceID="SqlDataSource1" DataTextField="DomainName" DataValueField="DomainName" Width="70px">
                </asp:DropDownList></p></td>
        </tr>
    </table> 
    <asp:Label ID="Lblerror" runat="server" Text="Label"></asp:Label>
    <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:DBHUSRConnectionString %>" SelectCommand="SELECT [DomainName] FROM [DomainName]"></asp:SqlDataSource>
    <asp:Login ID="Login1" runat="server" DisplayRememberMe="False" Height="162px" Width="377px">
    </asp:Login>

VB.Net code

    Protected Sub Login1_LoggedIn(sender As Object, e As System.EventArgs) Handles Login1.LoggedIn
        Dim connString As String = ConfigurationManager.ConnectionStrings("DBHUSRConnectionString").ConnectionString
        Dim DBConnection As SqlConnection = New SqlConnection(connString)
        Dim DBCommand As SqlCommand
        Dim DBReader As SqlDataReader
        Dim thisUserName As String
        DBConnection.Open()
        DBCommand = New SqlCommand("QGlobalUserRecords_sp", DBConnection)

        DBCommand.CommandType = CommandType.StoredProcedure
        DBCommand.Parameters.AddWithValue("@UserID", Login1.UserName())
        DBReader = DBCommand.ExecuteReader()

        Try
            If DropDownList1.SelectedValue = "AD" Then
                While DBReader.Read()
                    If Login1.UserName = DBReader("WM_UserName") Then
                        thisUserName = DBReader("WM_Comments")
                        Select Case thisUserName
                            Case "Agency"
                                Response.Redirect("~/Agency/Agency.aspx")
                            Case "Admins"
                                Response.Redirect("~/Admin/Default.aspx")
                            Case "STUHUSR"
                                Response.Redirect("~/Advising/StudentRecord.aspx")
                            Case "Faculty"
                                Response.Redirect("~/Faculty/Faculty.aspx")
                        End Select
                    End If
                End While
            End If

            If DropDownList1.SelectedValue = "ACAD" Then
                Response.Redirect("~/Student/StudentAssignment.aspx")
            End If
        Catch
            Lblerror.Text = "Database connection error. Please try again."
        Finally

            DBConnection.Close()
        End Try
    End Sub