I don't think using querystring is a good idea. However, i tried this scenario and it worked for me. I added 2 buttons and labels. On button 1 click, i generated a guid and stored it in a session variable and set it as text of label 1 and on click of 2nd button, i get the guid value from session and set it as label 2 text. In the output i can see both guids having same value. Here is the code.
protected void FirstButton_Click(object sender, EventArgs e)
var guid = Guid.NewGuid();
LblFirst.Text = guid.ToString();
Session["Guid"] = guid.ToString();
protected void SecondButton_Click(object sender, EventArgs e)
var guid = Convert.ToString(Session["Guid"]);
Label1.Text = guid;