Iceland would be sick!
Strong Nordic teams like those definitely a good idea to evaluate ourselves and learn from. They often play aerial (a big problem for us) and have very physically adept/natural athletes. Strong sides who've been consistent as of late and both Sweden and Iceland have beaten bigger teams in recent times, so it would be very good prep.
I like the thought of returning to some South American games, they usually end in draws or very narrow losses, then again that was under coaches like Piturca lol. I think we lost 1-0 to a Brazil with a young Neymar and an old and fat Ronaldo
the pearl of the new generation in and the other going out - how many teams could say they faced that kind of Brazil
The others were 1-1 with Uruguay, 0-0 with Argentina, and I can't remember with Paraguay but I think that was a tie too. Oh and of course there was the 3-2 with Chile even under Daum lol.
Of the bigger European teams, I'd like Portugal for sure, maybe England or France if not. Netherlands could be interesting too in their current situation.
If we do Asia, Japan for sure. They've been building their football up for years, their investment will pay off in the near future like Iceland's imo. It's a little tricky for them to get competing matches though being in Asia and all, they get less good preposition for World Cup but also almost guaranteed a spot each time.. anyway their disciplined, technical team would be good one to go up against and try and a play a nice football, maybe even take a leaf or two out of their book