I spent three weeks in Canada (BC) and USA (OR,WA) this summer with my 10III SFOS v4.6 roaming with a Finnish SIM (Telia). I was expecting some issues due to different frequencies, possible problems with LTE support etc. but didn’t really come across anything network-related. I used mobile data daily for messaging and browsing, sent/received the occasional SMS but did only very few voice calls. I had network selection on automatic and never attempted any manual configuration (not sure it if even was possible).
During the trip I had two issues with the device - on arrival to Vancouver my phone chose an incorrect timezone with the automatic selection; it ended up in Toronto time zone, i.e. three hours off the correct time. I think at that point it was using the Bell Canada network. Also, a couple of times the device UI slowed down when moving in dense urban environments - probably due to wifi being enabled and the wifi scanning slowing it down to a crawl.