MEA would most likely make a sweet addition to SkyTeam, but opposition from the USA might make that difficult.
I don't think the US would care.
From the US, you can buy a ticket to Beirut on Lufthansa, KLM, Air France, British Airways, etc.
joining Skyteam wouldn't be much different.
Not to mention that MEA
has ticket offices in the US and offers flights to Beirut through Air France from the US to Paris, then on MEA
or Air France from Paris to Beirut.
is MEA banned from Canada and Mexico too?
No they aren't. Although Canada did pull Air Canada's permit to fly to Beirut, there are no rules saying airlines can't fly to/from Beirut. Same with Mexico, although traffic between Mexico and Lebanon is almost nonexistent, so don't count on any flight happening anytime soon.
"Generosity is giving more than you can, and pride is taking less than you need." - Khalil Gibran