Dkiley, Ed white who used to be Federal member of parliament has done a lot of research on the ULSD issue. There is a webpage on it
HereDEF is not too much of an issue but you will go through about twice as much of it as you think and it is not available down there. There is also a company in Coquitlam, BC that will make your particle filter removable & cleanable.
According to Ed, the key is to drive under load as much as possible and avoid short trips to town and that sort of thing. Horizon Lussier a large RV dealer in Quebec who sell Class A Diesel pushers actually run their own caravan (They are the ones filling Telaquepaque RV in Lo de Marcos). Buy an RV from them and you get a free Mexican caravan. (you had better speak French) Obviously most of their customers are driving late model diesels. I have talked to their mechanic and he has no concerns. Also Pierre Blais who runs Amigos Rodantes caravans has a 2014 Mercedes diesel and he is driving it all the way to the Yucatan & back.