USA local SIM card

Hi All, sorry for possible off-topic, I really did not know where to ask this. I'm going to visit USA for two weeks. I want to buy a local prepaid SIM card mostly for IP access. Is it possible in USA to buy a prepaid SIM as a visitor, without long term contract? I need a public (can be dynamic) IP address, NOT over NAT, and (or) IPv6, if possible. My phone is GSM UMTS 3G. Expected traffic volume is about 10G. Will use it in New York City and Orlando City, not in rural areas. Good data roaming tariff in Cannada will be a big advantage. What can you advice? Thank you!