The C-series never was a contender.
For what it does for Delta it is way too capital intensive...

Boeing doesn't have the slots so they won't bid

Airbus can deliver and the 320Neo family offers significant fuel burn/seat improvements over our current jets to offset the capital cost.

I expect a mix of 320 and 321 and the 321 with shark lets might join the fleet in 2013 to replace the oldest 757s. The fuel burn/seat on the A321 with the current generation motors and sharklets is more than 15%/seat better than the 757. Later the GTF the A321NEO will offer even larger savings...

The 100-130 seater will come but it looks very familiar :-)
Just a new coat of paint and a concourse over...

Cheers
George