Brazil is every time favorite because they have good record in World Cup Matches but we can watch some good underdogs as well because now time is changing very quickly and many teams can give shock to these bigs
There are quite a few underdogs, who can give big shock to the favorites. Belgium is one of such underdogs. Others that come to my mind right now are Colombia, Uruguay, and Croatia.
IMO, Croatia isn't an underdog. They qualified to the WC by playing the playoffs, in one of their recent friendlies they lost against Peru (an inferior team), they only have two or three top players, the rest are just average...overall, it's very hard to put Croatia among the underdogs when they're clearly inferior to such underdogs.
About Belgium, i'm having a
déjà vu when people mention Belgium, same thing happened in the WC 2014 and Euro 2016 and both times they were a complete dissapointment.
Roberto Martinez has definitely made one of the most biggest mistake i have ever seen a manager make by not select Naingolan for the upcoming world cup whiles the likes of Fallaini and Januzaj all made the squad.He has since then retired from international football as a result.