Wirelessly posted (BlackBerry: BlackBerry8530/5.0.0.1030 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)
If you can find low-tier ("Saver") award availability on UA flights, then you can transfer your Amex MR points to Aeroplan, and redeem Aeroplan miles for travel on UA -- with no surcharges.