This offer has been around for a while, but I just found out about it as I was mapping out my elite qualifying strategy for the end of the year.
Stay 3 nights at any Starwood Property by December 9 and get an additional 3,000 Aeroplan miles on top of your normal Starpoints. Stay 5 nights and get 5,000 Aeroplan miles. If you happen to have 3 of those stays in Canada, then you can pick up an additional 3,000 bonus miles! So if you have 3 Starwood Stays in Canada and 2 elsewhere then you can end up with 8,000 Bonus Aeroplan miles on top of the SPG points you earn.
You still have almost a month to make this happen so if you are like me and planning some Starwood stays, then click here to sign up for this promotion now! You can also combine this with some other promotions such as the SPG 4Q 2012 Promotions for double or triple points and the iPhone booking bonus I talked about here. And if you have the SPG Amex or the SPG Business Amex and charge the hotel on them you can get an additional 2 Starpoints per dollar.
8,000 Aeroplan Miles may not be much by itself, but since they are a transfer partner of Amex Membership Rewards you can transfer over points you got from the 50,000 bonus on the Amex Business Gold Rewards card to get enough for a free ticket. They do charge fuel surcharges now though so you will probably only want to use the miles for premium cabin travel to make it worthwhile.