FlyerTalk Forums - book United flight with Aeroplan miles?

I'm so sorry...I'm sure this has been asked a million times, but there's just so many threads that I wasn't able to find the answer in a forum search.

I live in Canada and want to book a multi-city flight from YEG to NYC, then NYC to MIA, then MIA back to YEG.

I did a search on Aeroplan.com to book the reward travel. There is only one reasonable flight listed available from YEG to NYC on the day I want to travel, and it's terrible because (a) it leaves at 6am, and b) it involves a seven-hour layover. Also, there doesn't appear to be any non-stop flights for the second leg, from NYC to MIA.

I then did a search for award flights on United.com. In addition to the flight I found on Aeroplan (which is listed for 12K United miles, the typical amount I see for United awards flights that are equivalent to Aeroplan flights), there is another United award flight from YEG to NYC that's much better, listed for 18K miles. There are also several non-stop flights from NYC to MIA, which also cost a few more United miles than the minimum (15K to be precise). These don't show up on aeroplan.com or even aircanada.com.

So I guess my questions are: can I use my Aeroplan miles to book those "better" United flights? I'm guessing it will cost me a few more Aeroplan miles, but I'd be willing to do it if it's possible....is it just that I have to book by calling Aeroplan rather than doing it online?

Again, apologies, I'm sure this question has been answered multiple times...I don't know why I'm having such trouble finding it!