If Argentina met Portugal in the final it would be incredible. How the two countries that have two star players meet at the biggest football party in the world. Moreover, this is likely to be the last World Cup for them (Messi and Ronaldo). If this really happens this will be the most favorite match during the Qatar World Cup in my opinion.
Without a doubt it would be a historic game, as they never faced each other for the national teams. And it would certainly be the main game at the World Cup. But they can even meet in semi-finals, so if both teams are doing well, the probability of playing against each other is great. We'll see how things go in December, as the club season is halfway through.