The TripRewards hotel points program will give you 250 Air Canada miles just for enrolling. From a TripRewards email:

Between now and September 30, 2006, you’ll earn 250 Bonus Aeroplan Miles simply by enrolling in the TripRewards program and selecting “Aeroplan” as your earning preference. No purchase or stay is required.

The first screen is registration. Once you register you get to a preferences screen where you choose your earning preference — be sure to select ‘airline miles’. The default partner should already be filled in, but make sure it says Air Canada Aeroplan. Then enter your Air Canada frequent flyer number.