One minor thing to consider when looking at US cars is that they have less options as standard vs Canada... here we get Comfort Access, Cold Weather Package, Bluetooth/BMW Assist, Alarm, iPod/USB, Sunroof (for E90) all standard. Its a small thing but it makes a bit of difference IMO.
Not to mention the previous posts!
Current: 2013 Mercedes C63 AMG Sedan Magnetite Black / designo Porcelain/Black Leather
RIP: 2011 BMW M3 Sedan Alpine White / Fox Red Novillo Leather
Past: 2008 BMW M3 Sedan Melbourne Red / Black Novillo Leather