When I'm traveling to the US I just load up my Roam Mobility Card before I leave. It's a MUCH better deal than using one of the CDN providers with roam option.
This company uses T-Mobile network. I have not had a issue with coverage(a few yrs ago in VT it was pretty spotty, but other wise when I drive to NJ there is zero problems)
At some point in the past you could choose the City where you got a number from. Now it's a random location when you signup.
512MB per-day is plenty and if you do use it up it just slows down to 2G speeds afterwards. For Emails and GPS it's plenty.