They are not going to cancel your insurance, and certainly not without telling you. And the increase is going to be a percentage of what your current premium is. If it is just liability insurance, then it wont be as bad. But if you carry full coverage then your collision is going to go up a bit.
Also, the possibility of insurance getting cancelled will depend on if it was a DUI during a traffic stop or a DUI involving an accident. If there was an accident, then they can send it to underwriting and determine if they will keep coverage.