ATR42 - say 40 seats.
Twice daily Mon-Fri, once at weekends = 12 flights a week. (Fewer would make the route unattractive to business users)
12 x 40 = 480 passengers each way, each week, every week, even November and February.
That's a very big ask, especially at decent yields.
A few points:
Aren't RE due to get rid of the ATR-42's if/when the new 72's arrive, or will they retain one for the promised CAX-SEN and CAX-DUB services?;
Does the deal with at EI allow RE to operate flights in their own right, or will these be EIR branded flights (and what do EI think about that)?
I understand there will be no ILS at the re-developed CAX - how many flights will operate in November and February (OK, with current weather we'll add in June and July...)?