Did you rinse/soak the sand for 24 hours before you added it to your tank?
That is my first question, too.
How far above the substrate is the filter intake?
You could buy an AquaClear foam insert, put a set of deep cross-cuts in the top and slip it over the filter intake tube to help eliminate the sand, but it will significantly lower the efficacy of the filter. Another issue is that the impeller that moves the water through the filter can get terribly damaged and/or jammed with sand particles.
Also, as has been suggested, a properly placed canister filter intake should not be sucking up sand.
I wonder, though, just what type and gauge of sand you are using...very fine sand will easily get stirred up into the water column. From what I can see, the substrate that you are using is not very homogenous, but the exact size is difficult to determine as your corys could be anywhere from 1.5cm to 5cm. Also, how deep is the substrate, and what are you doing to avoid the development of anaerobic pockets in the sand?
I have run many sand-substrated aquaria over the past 38 years, and have rarely had an issue such as you are having, but iit is much easier to diagnose this sort of thing first hand than over the internet, so please be patient whilst we 'detective' this out.