Here's how you go to Sandbanks (pulls out trusty map). It's actually not north, it's east (on the way to Ottawa or Montreal).
Get on 401 EAST towards Oshawa. Keep going past Oshawa. Before you get to Belleville, you want to take the exit for provincial highway 33 (Loyalist Parkway). The direction is either South or East.
On the Loyalist Parkway (Highway 33) You will pass some antique shops and a winery (they have good chardonnay, it's called Peddlesden Wines). You'll get to a little town called Wellington. From there, you will see signs directing you to Sand Banks. If you get to the village of Picton, you've gone too far.
It should take you about 2 hours, maybe a little more, from DVP/401 to Sand banks.