Media for 2 cannister filters

That's a good question. Although I have no experience with this, I would put at least one layer of mech. filtration in each filter, to prevent the biomedia from clogging.

I'm doing and xp2 and an xp3 on a 55. As of right now I have one layer of bio (einhem bio balls in the xp2) one layer of micro filtration at the top of each fliter, one layer of carbon in the xp3, one layer of course foam and one layer of fine foam. Works fine, but I'm very open and interested to any suggestions from the veterans

I am using Eheim canisters, 2028 & 2229 on the 75G and 2262 & 2217 + 2 AC110's on the 220G. I set them up as specified by Eheim. You definitely want to keep the bio-media from getting clogged with debris so I recommend having sufficient mechanical media prior to the bio-media, except for the 2229, which is only bio-media.

Once the bio-media gets clogged, it will not perform as well so try to keep it clean.

I run an XP3 and XP5 on my 90gal. Both have pretty much the same media other than I only put Purigen in one of them.

If I were feeding CO2 into a tank through a canister, I'd probably emphasize mechanical filtration in that one.

I only run mechanical in the canisters. It's pretty much what they're there for in an established planted tank anyway. If you polish the junk out of the water, the remaining stuff your plants can and are happy to take care of.

the majority of my canister is filled with 6 for a $1 plastic pot scrubbers, these keep the water crystal clear.

I have eheims 2217&2028 in my tank and I removed some of the ceramic balls in 2217 to get some space for pillow stuffing, while 2028 have some ceramic removed for bag of purigen. I am thinking about adding more pillow stuffing or other sponges instead of biological media in the future. With dense flora, mechanical filter is all that you should care about.