A hot spot is like a cell phone in that it uses the cell technology, there will be areas with no service if you are off the beaten track in places. Verizon and AT&T probably have the best coverage.
I went with AT&T as they have GSM service which is the same as the majors in Canada and I could buy a Canadian SIM card from a Canadian provider if I wanted to use it at home, I can't speak about a US plan in Canada although it would probably be expensive as a US carrier would have to twin with a Canadian supplier. I stayed away with Verizon as they have a mix of GSM and CDMA service, not sure what service their hot spots are on. GSM is the world standard so a GSM hot spot could be used worldwide.
