Miller, and Millar, Canaletto, p. 24, challenge Ruskin's depreciation of Canaletto by questioning how many works of Canaletto had Ruskin had seen and closely examined. The implication is that his knowledge of Canaletto was inadequate to support such a case. It was noted by Links that of the two paintings of Canaletto to which Ruskin refers by name, the one said to be from the Manfrini collection is untraceable, and the one of the Salute in the Louvre is probably the work of Marieschi and untypical of Canaletto (see Constable, revised Links, Giovanni Antonio Canal 1697-1768 on No. 169). Moreover the 'bad landscape' in Turin ( Works, 16.186) which Ruskin believed to be by Canaletto was more probably by Bellotto. It may equally be the case that Ruskin's objections to the mechanisms of Canaletto apply more obviously to his later than to his earlier work (see Development of Canaletto's style).
That though is to miss the point. Ruskin was not aiming to give a balanced and objective view of the work of Canaletto - or of anyone else for that matter. He was aiming to draw attention to characteristic of Turner by contrasting them with examples of paintings which he considers to be the work of Canaletto - and at that level it is possible to provide support for Ruskin's case from work by Canaletto, however untypical it may be of his best work.