translating world position to (scaled) world-space canvas

I've been trying to position a canvas in world coordinates. There were lots of resources on this, but none of them yield correct results. I'm guessing this is because my canvas is scaled by the canvas scaler (for pixel-perfect art):

 int startX = i * tilegrid.chunkSize;
 
 GameObject stageStatsUI = Instantiate( ChallengeStageStats );
 stageStatsUI.transform.SetParent( canvas.transform, false );
 
 Vector2 destPos = new Vector2( tilegrid.tf.position.x + startX, tilegrid.tf.position.y );
  Vector2 viewportPoint = Camera.main.WorldToViewportPoint( destPos );
  // Vector2 viewportPoint = RectTransformUtility.WorldToScreenPoint( Camera.main, destPos );
 
 RectTransform rectTransform = stageStatsUI.GetComponent<RectTransform>();
 rectTransform.position = viewportPoint;
 //rectTransform.anchoredPosition = viewportPoint;

Any idea what I'm doing wrong? Thanks!