Highway Traffic Act section 158:
The driver of a motor vehicle or street car shall not follow another vehicle or street car more closely than is reasonable and prudent having due regard for the speed of the vehicle and the traffic on and the conditions of the highway.
Although not giving an actual defintion of what is too close to another motor vehicle, police officer and the courts in general us a measurement of one car length for every ten km/h of speed.
The definition of reasonable and prudent having due regard for the speed of the vehicle is open to interpretation by the court.