Ez pass and tt.. Which state to buy from?

Hi, I've done the route from the Canadian maritimes to Virginia beach and back with a single axle pup and now have an htt and thinking about doing that route again.. Or down to myrtle beach sc. Anyway, I found it very expensive for tolls and a total PITA ( pain in the a$$) for both the time to sit and wait for cash toll booths and to actually have small bills for all of that... Wondering about getting an ez pass. I've looked at few different states websites on it and don't see any rules that state that you have to be from a particular state or even from the USA to use this. Looks like they're happy to take the money. Maine even have "province" as an option in the billing address on their web-based form.
My question is: With a 2 axel vehicle towing a 1 axel trailer, which state is best to buy a tag from because it appears that the various states handle this differently... Some have a set-up for that and some don't . I most certainly would not want to cause violations or be mischarged.
Just wondering if anyone has shopped it out for that circumstance. Thanks