EF only shows award availability for select airlines of which US, UA and CO are not included. Full list is here
http://www.expertflyer.com/airline-upgrades-awards
US, UA and CO availability for awards can be found at their websites (CO - no login / onepass acct required; US and UA you'll need to first get a dividend miles or mileageplus acct setup first).
Alternatively, both US and UA availability should be uploaded into the Aeroplan website. Sometimes the aeroplan website doesn't show all available options on *A partners (especially for flights with connections), so a quick call to them can give you the clearest idea.