No routing allows a second intercontinental stopover in North America, only a second transit (though you can get 23 hours fairly easily). The advantage of starting your RTW outside of US/Canada is that you get 6 sectors for US/Canada travel (instead of 2). You might want to check the RTW price ex-Argentina, there is conflicting information but the last word is that it is priced in USD (and high). Your proposed routing is close to optimal given your objectives.