Do you mean on the Grand Canal? Or a quiet side canal? Or something in between?
For a very nice 4* hotel on a side canal, right near San Marco, try Hotel Splendid:
https://collezione.starhotels.com/it/i-nostri-hotel/splendid-venice-venezia/?gad_source=1&gclid=Cj0KCQjw5cOwBhCiARIsAJ5njuadRJOE3Na1y9iWg_diZiHb4DC78WptcAG1qGOcnXkJ4mS-3PDT7C8aArgrEALw_wcB
For a smaller, more modest 3* hotel on the Giudecca Canal, we liked La Calcina:
https://www.lacalcina.com/
That one used to be in Rick’s book, but maybe no more? The Giudecca canal is the large canal that runs between Dorsoduro and Giudecca Island. It is a broad view across lots of water, not a small intimate view across a small back canal. But pleasing nonetheless if you enjoy gazing at water.