There can be very little difference between taking fresh water from a major river that dumps into the ocean vs taking from the ocean. For example, if you took 0.001% of the flow of the St. Lawrence river and run it through an evaporative cooling tower you're doing very little harm and perhaps benefiting the local ecosystem through increased rainfall. If you took 50% of the flow it'd be a problem, but the St. Lawrence is massive.
People think water is scarce, but there are still parts of the world where water is abundant, where flooding is more of a concern than fresh water scarcity.
Combine with Quebec's cheap electricity, and it seems an ideal place to site data centers.