That's not really true any more, the few teams that still have both an aero bike and a lightweight bike only end up using the lightweight one on incredibly hilly stages, and even then only with a hill finish as the aero bike can give you an advantage on a descent. Most teams just ride bikes which are a mix of both now though, with aero technology but light enough to be within a few hundred grams of the weight limit.
collett's point could be important. And difficult to tell as you can't ride them first. Are you set on Canyon?