I'm a dual US/Cdn citizen as well, have been a Canadian resident for 7 years now and always play the passport game when crossing into either country (I'm a US citizen when travelling to the US, Canadian when coming back to Canada). From what I've heard & read (on FT and otherwise), each of those countries requires its citizens to present themselves as such, regardless of residency. Have never had problems with checking in for flights either...the agent swipes the passport regardless if I provided advance information and I think it overwrites whatever previous entry was there on the outbound leg. The only "benefit" I can think of is that entering the USA allows you to use the USA citizens line which is often much shorter when preclearing in Canadian airports. Nexus pass eliminates all these issues though!