Does a creature enchanted with a Control-changing aura still count as being under the enchantment owner's control for attacking purposes?

Control of a permanent is determined by the current game state, not by who owns attached Auras. If a Control-changing Aura (such as Control Magic) transfers control of a creature to its controller, that player — not the original owner of the enchanted creature — now controls the creature for all game purposes, including declaring attackers.

Under CR 509.1, only the active player declares attackers, and only with creatures they control. 'Control' here means the player who currently has control of the permanent as established by continuous effects (CR 613), not the original owner or the Aura's owner.

The Aura's owner is essentially irrelevant to this question. What matters is whose control the creature is currently under as a result of all applicable continuous effects. The Aura creates a control-changing effect (CR 702.2 does not apply here; the relevant rule is CR 613.2 for control-changing effects), and that effect determines the controller.

Concrete example: Your opponent controls a 3/3 Grizzly Bears. You enchant it with Control Magic (you now control the Bears). On your turn, you — not your opponent — may attack with those Bears, because you control the creature. Your opponent cannot attack with it at all while your Aura remains.

If the Aura leaves the battlefield, the control-changing effect ends and control reverts to the original controller (CR 613.5), at which point your opponent may attack with it again on their turn.