Classification must be based on creditors' legal rights vis-Ă -vis the debtor under the CCAA; subordinated debenture holders did not possess a materially different legal interest vis-Ă -vis Stelco (only contractual subordination/turnover obligations), there was no realistic conflict of interest affecting the debtor-vs-creditor relationship, and the supervising judge did not err in law or in exercising discretion in keeping unsecured creditors in a single class.