MOD EDIT: Dev statement courtesy of NintendoWorldReport:
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http://www.nintendoworldreport.com/news/31492
The CEO of Straight Right, Tom Crago, has told NWR that, "The game will run at 720p."
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The Wii U will be getting the mass effect possible on a console.
For the first time on a home console, Mass Effect 3 will run in full 1080p resolution, according to September's Nintendo Power, issue V282.
The article has also re-confirmed that the extended cut of the ending sequence and other various DLC characters and weapons for the four player online co-op mode will also be included on the disk.
Mass Effect 3 for the Wii U is currently scheduled to release alongside the Wii U at launch.
http://www.nintendoworldreport.com/news/31492