Americans returning home by international flight connections through Canadian airports can look forward to easier transfers, according to this article in the national newspaper Globe & Mail. https://secure.globeadvisor.com/servlet/ArticleNews/story/gam/20121204/SRMOBILITYAIRPORTSATL

Both Toronto and Vancouver gateway airports have had advance US immigration and customs procedures for some time. But the process required some if not all passengers to pick up their luggage and take it through both Canadian and US checkpoints. In Toronto’s large Terminal 1, new baggage screening equipment will eliminate the need to retrieve bags. It could be operating in 2013. The need to go through Canadian border procedures first has already been eliminated there. Terminal 3 will be stuck with the old routines for awhile.
Vancouver, a gateway for Asia, pre-clears passengers through Canadian customs so passengers can go straight to US customs there without picking up their bags, the report says. However, that improvement is restricted to six airlines, listed in the article.