Based from the previous MCU 3quels, Guardians 3 is unfortunately the only 3quel that isn't outgrossing its predecessors in North America. While Ant-Man 3 failed short from outgrossing Ant-Man 2 in North America, by 3 million which is too close. That should have been easy for Ant-Man 3 since it opened higher.
Avengers 3 - 678 vs A1 623
Spider-Man 3 - 804 vs SM2 390
Thor 3 - 315 vs T2 206
Captain America 3 - 408 vs CA2 259
Iron Man 3 - 409 vs IR1 318
Ant-Man 3 - 213 vs AM2 216
Guardians 3 - 250? vs GOTG1 333
Looking at those numbers, its a bit alarming especially for a franchise that plans to release 3 to 4 movies every year for the neXt 5 years.
This should serve as a big lesson to Marvel Studios, moving forward. Last year, DS2 easily outgrossed DS1. While T4 outgrossed T3 in North America. I personally focus more on North American boX office than worldwide numbers since NA is the #1 market for Marvel movies. I think its eXpected that Marvels won't come close to outgrossing CM. I'm not confident it wouldn't even hit the $300 million mark in North America. So over all, the boX office numbers this year for Marvel Studios would be down compare to previous years and I doubt Disney bosses would be happy.