ActiveDocument.PageSetup.Orientation refers to the document. If you want to refer to a page then set a range to the page and check the pagesetup of that range or put the cursor in the page and then Selection.PageSetup.Orientation will return 0 for Portrait or 1 for Landscape. To iterate through the tables and process only those on a landscape page
Dim oTable As Table
For Each oTable In ActiveDocument.Tables
If oTable.Range.PageSetup.Orientation = wdOrientLandscape Then
oTable.Cell(1, 1).Range.Text = "Landscape page" 'do something with oTable
End If
Next oTable