Canaletto 's primary reputation was for truth, and in particular for truth about Venice.
Constable, revised Links, Giovanni Antonio Canal 1697-1768, pp. 9-10 quotes Orlandi (1753) on Canaletto developing his ability when in Rome'di copiare e contraffare con tanta perfezione la natura ed il vero'. 'His excellence lyes in painting things which fall immediately under his eye,' is a frequently quoted sentence from the letters of McSwiney to the Duke of Richmond. When William Beckford arrive in Venice in 1780 he felt himself already familiar with it, and description was 'superfluous' because 'the pencil of Canaletti conveys so perfect an idea' ( Beckford, Italy with sketches of Spain and Portugal I, 101).
For Mrs. Piozzi / Thrale in 1785 ( Piozzi, Observations and reflections made in the course of a journey through France, Italy and Germany, Vol 1 p 150, and quoted in Miller and Millar, Exhibition Catalogue, London: The Queen's Gallery, Canaletto, p. 24) seeing the city 'revived all the ideas inspired by Canaletti, whose views of this town are most scrupulously exact;... to such an extent indeed that we knew all the famous towers and steeples &c before we reached them'.
Cook, Handbook to the National Gallery, including Notes Collected from the Works of Mr. Ruskin, p.325, suggests that by the end of the nineteenth century there was a change in Canaletto's reputation as a result of Ruskin's depreciation of Canaletto, and 'that the Venice of all the most popular painters today, of whatever nation, is the Venice of Ruskin and Turner'.