After your comment:
Sorry, I misremembered. I should have said
Intersect
.
You have a rectangle that you have drawn. You can get the Bounds property of the controls in turn (search for 'c# iterate controls') to find out how, which is a rectangle. Then for each control use:
if (Rectangle.Intersect(myDrawnRectangle, controlBoundsRectangle) != Rectangle.Empty)
{
}
Good luck! :)