I don't know if it was intentional on Hasbro's part to release the MARS movie preview three pack to Walmart Canada when they did, but after reading the latest GIJoe Collectors Club newsletter---it states that the MARS set is an online only exclusive and wont be available until June. They even boast that will be a full month before the other figures hit the shelves.
Meanwhile, our Walmarts have had the figures stocked since late March.
Bonus! and about time we get something first.