I’ve had two Canadian friends recently become US citizens. The US did not require them to give up their Canadian citizenship. They actually wanted to, and were prepared to renounce their Canadian citizenship, but it was totally unnecessary, and no one in immigration (or whatever the department is) even wanted to deal with them on that issue. So they’re dual citizens now. I think that’s strange, and I wonder if it’s like that for most countries, or if Canada is more of an exception to the rule.
That’s common, their Canadian citizenship is governed by Canada, who may or may not let them give it up. But they’d be dealing with Canada, not the US. My guess they would, but many countries won’t or will do so only limited circumstances due to things like mandatory military service. Cuba doen’t recognize dual citizenship, as far as they’re concerned any American citizen born in Cuba is Cuban, period. Forever.