The C-series is projecting 15% cash operating economics on 20% better fuel burnsto current a/c. Somewhere hidden in the small print is the issue that the purchase price or the trip costs are higher than the A320neo or 737max... i'm not sure which one.
The best aircraft of all for LCC ops (on 2-4 hour sectors) is the 737-800max when you look at cost per seat, cost per trip and cost per a/c acquisition. The term 'pile them high sell them cheap' is there for a reason! But I can't see easyJet going back to boeing after having ditched them only a while ago.