Most manufacturers offer a 125 amp breaker option, some even go higher. I have 150 amp breakers going to my garage subpanels.
In your situation it probably makes sense to put in a 125A circuit to the sub instead of 100, and then you can put two 60A breakers in, one per car and not worry about load sharing. That allows you to run the Gen 3 station and a
https://evcharging.enelx.com/store/residential/juicebox-48, 48A OpenEVSE or any other number of 48A stations.
That should give you max flexibility for two vehicles over the long haul.