Lets assume, despite all odds to the contrary, some foolhardy Romans somehow end up in the Americas. In what regions are they most likely to land?
In order of likelihood (with the likelihood of any crossing being extremely low):
The West Indies, the repository of the Atlantic currents?
The
volta do mar will assist any crossing, whether that crossing is planned or not. Roman knowledge of and trade with the Azores/Canaries - which, if I remember correctly, you've suggested in the past - could put Roman vessels in the right place.
Brazil, with its relative proximity to Africa?
A Roman coastwise trade to the Bight of Benin for gold, ivory, and slaves - perhaps because the existing trans-Saharan trade routes have been disrupted - could lead to an accidental discovery of Brazil.
(To be honest, it's pretty much accepted that Cabral sighted Brazil during his 1500 follow-up to the de Gama voyage only because of reports of Columbus' earlier voyages. Cabral swung much further west than necessary knowing the
volta do mar would still bring him back for his planned voyage to the Cape of Good Hope.)
The Canadian Maritimes, where the Vikings landed?
A high latitude voyages is the least likely of them all. The Romans simply didn't travel there for trade or anything else.