That's gonna be a real tough match up because of Ike's slow tilts and mac's super armor. I'd recommend trying to do short hops air dodges to close in the distance to get to grab and trying to do cross ups with neutral air. Forward air if you're hitting it with enough height can be good for jump ins I suppose. Also, you're gonna have to spot dodge those f smashes and go for a jab combo. Back airs are gonna be real good to catch them by surprise, try doing them retreating and as advancing.
The most important things are gonna be. Never try trading with him, you'll lose. And never let him get back on stage. Fair is gonna be great, but you'll also want to anticipate air dodges and go for the delayed dair.