I don't "do" rules (as you may have noticed), but the correct usage is "the weekend."
Perhaps it has something to do with the difference betwen a proper (capitalized) noun and regular noun. Compare, "I will ask the son of the owner" versus "I will talk to John" and "I am going to the city" compared to "I am going to Chicago." Or "I see the planet" versus "I see Mars."
It doesn't always work, of course. "Look at the tower!" "Look at the Eiffle Tower!" or
"I took a cruise on the ship." "I took a cruise on the Serenity."