Beans: how many cans? Drained?

I don't think it matters what brand of beans you purchase. I would recommend a dependable, good quality brand or whichever is your favorite brand. You will be seasoning these beans and warming them up to spoon into tacos. So you want an unseasoned brand. I'd also drain them before heating, because otherwise you will end up with a bean soup of sorts that is much too loose to be contained in a tortilla shell and eaten out of hand. As far as how many cans, that depends on how "beany" and filled you like your tacos to be. I imagine the recipe writer has in mind only 1 can, but there is no reason you couldn't use 2 if you preferred.