The best place on the web for this question, and for many reviews is
www.gpspassion.com
I personally use Inav Corp Iguidance and like it, TomTom is the other leader. I use it around Northern California but I bought it last summer when I lived in Washington, DC, All over the east coast and transcontinental trip it worked great.
I disagree with your assessment, most of the MAJOR GPS firms do nationwide and Canada (North America). This includes, microsoft, Delorme, INav, TomTom, etc