As long as the AMEX-Aeroplan-US trick still works, you can convert 10K AMEX MR points to 10K Aeroplan miles, and convert them to 8500 US miles via points.com. Then book on UA with your US miles. Blog post here
http://thepointsguy.com/2012/08/how-...-decent-ratio/, there are also posts in the related threads here on FT.