For a canister filter, usually you don't hang it at the back unless it's a very small canister.
They might be too heavy for you to hang at the back unless you are sure that your tank is strong enough to withstand the weight.
If your tank has a frame, then it might be ok to hang it.
For a frameless tank, there is a risk if the filter is too heavy.
Usually you put it under the tank(for two tiers stand), or inside the cabinet or on the floor.
If your table/cabinet is wide enough, then you can put it at the side (left or right).
I attached a photo of how it looked like if you were to put it at the side of the table, provided your table still have space at the side.
I guess some of the smallest canisters are Shiruba XB-305, Eheim Classic 150 or Oase 100.
I like Oase 100 flow rate as it's more powerful and better than Eheim and Shiruba.
It's also easier to clean as the filter pads/medias are not stack on top of one another.
The filter medias are put side by side making them easier to take out for cleaning.
You can check the dimensions from the websites below:
The FiltoSmart 100 external filter has a compact design with a large filter surface, perfect for marine and freshwater aquariums. Utilizing biological and mechanical filtration, this external filter, ensures effective water filtration and optimal living conditions for aquarium inhabitants.
1. It can be used as hang-on or external canister.Large filter box, additional with multiple filter materials.Separate inlet & outlet design allows water to flow to and return without bypassing filter media for optimized filtering effect. 2. The body is made of highly durable ABS plastic to...
I have an Oase biomaster thermo with stainless steel lilly pipes on my 100 liter tank. I like this filter because it has the heater in the canister so saves on equipment in the tank. The pipe work is really neat and the lilly pipes take up very little space - the pipes are 16mm fittings so you would only need a bit more space to manouver them into the cabinet.
When looking for a canister filter its best to look for something that will give you 10x turn over (unless you have fish that specifically need low flow like a Beta). So ideally something that will do 1250 lph.
A 29g tank is not large, and a canister would not be my choice for a filter since the fish suited to this size tank are not likely to appreciate strong currents. But that means you need to consider the fish species, and then decide on the appropriate filter. I have a dual sponge on my 29g but it has quiet blackwater fish species. I have used a small internal filter like a Fluval Quiet Flow if more water current is required. But the fish should be the deciding factor.