You won't fare any better than using Aeroplan with Mileage Plus:
"Discounted flights within Canada—50% of actual, paid miles (or 250 miles minimum) " (from UAL's website)
Tango fares have been discussed elsewhere. It is likely that you will get 50% miles AND (unlike with AC) these would count towards status.
http://www.flyertalk.com/forum/showt...t=tango+status