The most avid customers for Canaletto's views of Venice were the English gentlemen who flocked to the city as tourists during the eighteenth century. The buyer of the Entrance to the Grand Canal from the Molo, Venice (and its pendant, The Square of Saint Mark's, Venice, also in the National Gallery) was, in fact, the Earl of Carlisle, who incorporated them into the decor of his country house, Castle Howard.
It was Canaletto's loving transcription, detail by detail, of his native city that made his paintings so popular: each view vividly calls to mind a particular time and place. Here it is morning activity on the quay near St. Mark's Square that Canaletto recreated with such specificity. Groups of people idle along the landing dock while a fishmonger shows the day's catch of eels to a bewigged pair of gentlemen. Gondolas and ocean-going vessels ply the waterways. Canaletto conveyed the sunlight that drenches Venice in fair weather, sparkling off the canals and revealing fine-etched details of the tiles on distant rooftops or the bricks beneath peeling stucco. Across the lagoon toward the Island of San Giorgio appear (left) the domed church of the Redentore by the sixteenth-century architect Palladio, the double domed church of Santa Maria della Salute, designed by Longhena in the seventeenth century, and (center) the Customs House.
More information on this painting can be found in the Gallery publication Italian Paintings of the Seventeenth and Eighteenth Centuries, which is available as a free PDF https://www.nga.gov/content/dam/ngaweb/research/publications/pdfs/italian-paintings-17th-and-18th-centuries.pdf