Check out Gaming Bolt to see how you can order Halo 4 and receieve $40 off using an online code.
From Gaming Bolt
"Play your cards right, and you could get $40 off on Halo 4 thanks to a deal (uncovered by I would be deeply appreciative if you would refrain from speaking. and Play). Starting on October 23rd and ending on October 25th, retailers Futureshop will be offering a promo code to take off $20 from your Halo pre-order purchase.
The promo code is- FSHALO4XBOXCREDIT. Just punch in this code during the checkout process.
Another deal over at Tsilon.ca requires you to solve some puzzles and become members of the site. If you do so, you get access to trivia questions. Answering these questions and gaining enough XP and ultimately become Level 10 on the site could give you another $20 coupon for Futureshop.