Raycast 2d Isn't going Like I want it to

You named your variable "direction" but that doesn't make it a direction, it's a point in space.

Here's the docs for Physics2D.Raycast. The 2nd argument is a direction not a position in space. In your case it's a normalized "direction - startPos" but be careful here as those are 3D vectors. You should use 2D vectors otherwise any differences in Z can throw it out.

There's Physics2D.Linecast which performs a check on a line-segment.

 

Okay but that's why we have docs. You specify a start position, direction, distance and mask.

Code (CSharp):

1.         startPos = playerTrans.position;
2.         mousePos = cam.ScreenToWorldPoint(Input.mousePosition);
3.         direction = (mousePos - startPos).normalized;
4.  
5.         RaycastHit2D WallCheck = Physics2D.Raycast(startPos, direction, Mathf.Infinity, ground);
6.  

Also note that unless you are absolutely sure this raycast will hit something, you should check to see if it does with "if (WallCheck) { <DO SOMETHING> }"

Sorry yes, I just saw that you were transferring the Vector3 Transform.position to Vector2.