Water loss from a canal is negligible compared to the amount of water in the air.

What's interesting is that the way we build canals and other similar structures that allow natural runoff to pool on their uphill side instead of continuing downhill has led to large vegetation growth:

https://m.youtube.com/watch?v=jf8usAesJvo

The water percolating and increase in transpiration from the plants in these areas has way more effect on the local climate than the evaporation directly from the canal ever would.