It's apparently not all that simple. According to recent research, CBC reported that exercise won't stop sitting all day from potentially killing you.
That is because sedentary behaviours for long periods of time can increase risk of colon, endometrial and lung cancers. Research shows that for each day, every 2 hour increase in sitting time saw an 8% increase in colon cancer, 10% increase in endometrial cancer, and a 6% increase in lung cancer.
Link to journal here.