I do not think Guardians or Justice League are the competitors to be #2 WW, but, as @Valonqar and @FantasticBeasts say, F8. I have JL with a slim chance to make 1b and Guardians making maybe 1.1b, but not as high as BatB, which seems headed to about 1.25b, unless Japan explodes.
On the other side, a film that has a probable $350-400m foreign market is really hard to compete with. And although a drop seems unavoidable in consolidated markets, Furious saga seems to have more appealing in developing markets. Beyond the 390 million in China, F7 did 46 million in Brazil, 51 in Mexico or 34 in Russia with already shit ER. $523m from 4 markets and I see hard F8 can drop in those countries. I could easily see a 275/950/1.225b scenario, which seems enough menace to not lock the #2 WW spot for BatB.