How many CCs is online play?

Solution 1:

According to the Wiki, it appears to be based off the your/your opponents VR (Versus Ranking):

Between 1000 and over 4000 VR when playing Worldwide or Regional VS. Race, players race at 100cc, and starting at over 5000 VR, players race at 150cc.

A few GameFAQ threads also discuss this, such as this one, though they state at around 3000 VR is when you start seeing changes:

At 3000 VR ish I started getting put into 150cc games.

Another GameFAQ:

After hitting 3000 and being placed in a room with all players being 3000+, it's 150CC. Before 3000, it's 100CC.

It looks like the starting CC is 100. And from there, it increases depending on the VR of everyone.