While I truly wish they would, its EXTREEMLY, unlikely.
EPIC games hasn't made a habit of giving out demo's, and gears of war (and other games in the genre) aren't exactly known for "demo material". So I would say no, but there's no official news so theres always a chance
um they probably will but it really depends if there planing on puting th egame on demand then definitly but if not then its anyones guess but if you want a couple good trailers of like gameplay then just check out gears3 fan sites