Hi Carlitony,
Welcome to FlyerTalk
There is a primary point I think you are missing here and that is: Air Canada and Aeroplan are different companies. Air Canada buys miles from Aeroplan to award you for flights etc.
So you are right, the websites don't work super well together, but that is like asking my Visa rewards card website to work better with Amazon. It would be nice but it may not happen.
As for saving the aeroplan number, I use Chrome and have no problem doing so.