In the South East, they bring you sweetened (usually far too sweetened for my tastes) iced tea. This is amazingly universal.
I live in NC and have been probing the border for years.
For “nicer” restaurants, the universal sweet tea boundary seems to be precisely at the NC/VA border.
In this chunk of the Southern Cone they’ll probably assume that you want this:
Cold and sweetened yerba mate tea, often flavoured with lemon or peach. It’s actually quite good, preferable over soda.
Brazil?
Yup. I’m not sure if the same tea +→ cold yerba mate tea implication applies elsewhere in Brazil though; in some places I’d expect a “this is a restaurant, if you want tea go back home” or similar, dunno.