I have converted from MR to Aeroplan but always wait until bonus time. There is a 20% bonus happening right now so now is a good time to do it. You can convert to your own account or you can convert to someone else's account. When you do it online they will just ask for the number of the account you want to convert your MR points into..... that being the Aeroplan account that you wish. I have never converted the other way nor am I sure you can do that.