Not sure how long it's been there but just jumped over to ac.com pass site and noticed this new New York Weekender Passs is available in Tango for $549 for four credits for travel BETWEEN Montreal, Ottawa or Toronto AND Newark or New York. More info:

Get four (4) flight credits
Travel on Saturdays and Mondays between eligible cities for a twelve-month period
Earn 25% Aeroplan Miles for distance flown
Anytime changes online for a $60 fee
Same-day changes for only a $150 fee
One easy payment at time of purchase
Get one (1) Aeroplan Mile for every $3 spent
Flight credit bookings are subject to availability for the Tango fare option (K booking class)
Plus, save up to 40% on your hotel stay in New York and make advance arrangements for entertainment and transportation.