The best place to ask this question, unless there is some unique Canadian perspective I am missing, would be on the DL or AA forums.
Speaking for myself, as a DL PM, the upgrade system is different (less certificates, only earned once a year, but can upgrade using miles), and you do face the fact that you will have to go via JFK or ATL (or sometimes CVG) if you want to travel overseas, as opposed to possible direct flights from Canada.
Simon