Yes, rebellion is still possible, even with units inside the province, but the possibility of successful rebellion is greatly decreased

Easy way of checking is briefly ordering your troops to move - and then check the increase in chance, before cancelling the move order.

Generally you need infantry but it can be assisted by armor or other troops. The insurgency chance is reduced by the modified defense strength of garrison units in town/province.

Although even provinces can rebel, it is very unlikely since we changed the formula from COW.

If an insurgency occurs, 1-3 insurgent units spawn to fight the garrison. Only AFTER they have overcome the local defense forces does the city/province flip to Rogue State control.