On a 70g a canister would be a great option. If you really wanted to concel the intake and exhaust tubes of the canister. You could have a couple of holes drilled into the bottum of the tank and install bulkheads, prior to set up. Have the intake tube to where it just sticks up past the substrate. Do the same for the return. Depending on the return you choose (spraybar or jet) you could hide them with rocks, driftwood, plants etc...
If you really wanted some awesome filtration, you could do the same thing with a wet/dry sump. Building a 20 or 29g sump for a 70g tank would really increase your filtration and bioload limits. Not to mention a DIY
sump can be built cheaper than the price of a large canister filter.
Check out this site. if you do some research and get a basic understanding of sumps, they really are'nt that confussing or hard to build.
Edit: I forgot to mention. With a wet/dry filter you can place the heater in the sump. Eliminating another piece of equipment in the tank.