Cannas are not fussy about soil texture or aeration but rhizomes will be easier to dig and clean with a loose textured soil. There is some reason to believe that cannas benefit from soluble silicate. You can both loosen the soil and add soluble silicate with parboiled rice hulls (PBH). If you can buy and pick up PBH from a local grower's supply, e.g., BFG, http://www.bfgsupply.com/, it will probably be cheaper than peat moss, otherwise, the shipping charges will kill you. PBH lasts as long as peat moss in the soil before it visibly disintegrates. That's about 2 years in the Chicago soil.