Anything is possible for enough money but I don't think you understand how much money what you're proposing would cost. In electricity alone desalination costs around 3kwh/m^3. 3.7mwh/acre foot of water. Last year we got 9.2 million acre feet of water in the Colorado River of the allocated 15 million acre feet. So if we say we want to supplement flows with just 2 million acre feet of desalination water, that's 7 Pwh of electricity. Per year. That's approximately 1000x the annual generated power of the largest nuclear plant in the world.

And we haven't even pumped that water 3700 feet up from sea level to the elevation of lake Powell.