There are 2 companies that provide iPad service in the USA and I think Canada one is Verizon the other is AT&T. Your friend should contact them to see if they do as a pay as you go service, but I'm afraid my gut feeling is no.
iPads sold in the USA are supplied with one of these sims, but on a contract basis only.
Worth contacting them, and also his / her present service provider. Remember if they are staying somewhere with wifi access they can use that for a much cheaper cost.