2 issues - without a US address, you essentially can't buy, insure, and register a car here. You also can't rent a car in one country and drop it off in another.

My best suggestion would be for you to KEEP one of your cars and use it for the duration of your US road trip. Then buzz back across the border and sell it in Vancouver.

I don't think the Ipad and 3G are worth the expense - even Motel 6 has wifi now. Most of them charge 3 bucks a night per machine, but you could also stay at Super 8's, which all have free wifi. There are also other budget chains and most have wifi.