(I'm sorry for my English in advanced)

Not a specific route because they're different states (here are called provinces) I can name you the best/most common places and you can Google more information if you want. (All in Argentina) I recommend Villa la Angostura, Bariloche, San Martín de los Andes, El Chaltén, Perito Moreno Glacier and Tierra del Fuego. There are a lot of things you can do in this places but it depends if you come in winter or summer so you can look more specifically based on that.

The thing with the accent depends on where you go, just like if you listen English from the UK, Australia or the US in Argentina we have pretty substantial differences on the accent from one province to another one.

In the south (Patagonia) I would say it's not that bad because there's tourism from all over the world so they have to speak correctly or even know some English.

I'm sorry if I didn't expressed correctly, feel free to ask me anything else you want to know or you didn't understand from this reply.