I don't really have trouble with this MU TBH. This and Pika are weird MUs to me in that while they feel like they should be even, I tend to find them really easy for some reason.
First off, inhale is not that hard to land in this MU, especially since D3's seem to use their inhale, and our inhale ALWAYS beats theirs unlss they are coming from above you. Also, when you inhale them, you have a choice in that you can keep your inhale for the inhale break footstools and gimping his UpB (remember, inhale breaks count as grab releases, so if he uses his jumps and UpBs, then you inhale him before he hits the ground, he doesn't get his jumps back), which can reall help out since they can end a stock MUCH earlier than what we usually do, or get D3's inhale, which has more range and I think does more damage.
Utilt is amazin in this MU, as is Dair IMO (big character = get shieldpoked). Of course, you're both going to grab a lot. Make sure to watch for the Utilt as soon as you get around 110% or so. His Bair beats ours, but if he tries to FF Bair from above for some reason, Utilt beats it.
Tech his Dthrow, otherwise he gets a free Ftilt, however keep in mind that he can tech-chase you from that, so mix it up.
Yeah, not sure what else to add, but I think I'l get to play Seibrik this afternoon, so I'll add more then.