In response to the Air Canada promo, WestJet has released a 20% off coupon code.

WestJet Plus

Fine print:

Promo code: WJP72
Coupon code: NXRXJGF
Book by: December 30, 2014 (9:59 p.m. MT)
Travel from: January 7, 2015 to June 15, 2015
Blackout Dates from: April 1 to 7, 2015 and May 14 to 19, 2015
How to get this offer: To redeem this offer on, both the promo code and coupon code are required at time of booking. Percentage is applied to base fare excluding taxes, fees and charges. Taxes, fees and charges are extra. Promo code may also be applied on a return flight with the same restrictions. Discount can only be applied towards fares displayed in the Econo category.