I would say it’s 50/50 joking and serious. There is some major hate down there.
I think everyone can agree that Mexican politics are ridiculous. They hate their politicians more than we ever could. US politics with my family is a little tricky. They hate Trump but actually agree with him on some issues. Weird and complicated.
As for the sponsorship/“get me across the border” issue, I would say ~90% are dead serious. The people I barely know are mostly joking. I’d say only ~10% of them are at all serious about it.