The WJC is known in Sweden but I wouldn't call it popular. Casual fans don't care at all but hardcore fans do.
In Sweden the popularity of hockey is probably something like this among non-hardcore fans
SHL/Allsvenskan > Olympics >> WHCs >>>>>>>>>>>>>>>>> Other national team tournaments (EHT/WC) (somewhere after here causals stop caring) >>>>>>>>>>>>>>>>>>>>>>> WJCs >>>>>>> NHL >>>>>>>>>>>>>>>>>>>>>> KHL/Other leagues
There's a lot of people that cheer for their hometown clubs or clubs that are close to their hometown/where they live, even if they don't always show it. You can ask most Swedes about which team they like and almost everyone will have an answer for you, even if they aren't that into hockey.
During the Olympics it seems like most people cares, especially further into the tournaments, same goes for the WHC if Tre Kronor does well. Then you can hear people talk about hockey on the streets/in the subway/on the bus etc but when there are no tournaments you almost never hear people talk about the national team or hockey in general.
WJCs is big among the more hardcore fans, mostly the same people that cares about prospects or the NHL. So it is quite a small minority of swedish hockey fans that really cares, at least compared to other kinds of hockey. It is growing though, SVT has really helped to make it grow, junior sports usually isn't popular at all in Sweden so I'm a bit surpised about that.
As an example, all my close friends have SHL teams that they cheer for but they almost never watch hockey (except for when it's the SHL-playoffs, then they might watch a game or two), most of them watch the Olympics if they have time and the WHCs if Sweden goes far (Semi-finals or final), one or two of them have gone to EHT a few times "to watch Tre Kronor" and they have caught a WJCs game sometime as well due to Sweden doing well but I've never heard any of them ever mention NHL or any other league, I would be surprised if they have seen any non SHL-games at club level ever.