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this might be a dumb question but i was wonder if your tank has to be at certain height in order for a canister filter to be used? my tank is in a little(but not that little) cove and the tank top is at 30 inches above the ground. could a canister filter work here?

I wondered about that too. I have a 125gal tank sitting on the floor (no stand) and a fluval 404 sitting right beside it. It works just fine. A few people told me that it had to be 2 to 4 feet below the tank to work but it really doesn't.

I suspect that the reason why it is better to have the filter situated lower than the aquarium is that due to the lower pressure in the filter/pipes (pump is sucking and the water is moving which both cause a lower pressure) a small amount of water evaporates. Over time this creates an air bubble that passes through the pump which can harm the impeller.
When the filter is located below the aquarium, the pressure of the water prevents any evaporation and no air bubble is formed in the pipes/filter.
(Note that I am not certain why the water evaporates, is it because of lower pressure or just 'normal' evaporation that always happens? This is not very important, the important part is that placing the filter lower reduces/prevents evaporation due to the extra water pressure)

A few years back I had the filter on the table next to the aquarium. About every hour or so you could hear the pump making noise when an air bubble passed through the pump. Now the filter is located under the aquarium and air bubbles are never formed in the filter anymore.

Canisters work on gravity. I initially had my XP3 under a table with the tank on it, and the filter was virtually silent. When I got a stock tank, the XP3 was placed on the floor next to it. It does a good a job as when it was under the table, BUT it is noisier and harder to prime. I have also read that there is a risk of burning the motor out sooner when the filter is used this way. But, people do it, and I've not really heard of any issues other than the ones above.