BioWare has announced a single-player and multiplayer Mass Effect 3 demo.
It's due some time in January, well over a month before Mass Effect 3 arrives.
Owners of Battlefield 3 and its Online Pass will, via their EA Account, automatically gain early access to the Mass Effect 3 demo. PC copies of Battlefield 3 bought on Origin automatically have the Online Pass.
An online tool will be released enabling you to check whether your EA Account has been granted early access.
BioWare will announce another, free way to gain early access in "late November or early December".
How long the early access period will be is officially TBA.
The exact Mass Effect 3 demo release date will be announced in late November.