In short, yes you can create the animation/movement in Alias, but given that the average cabriolet roof isn't a "simple" movement (with parts folding into/onto one another) it will prove to be quite difficult. Even if you do manage to animate the roof in Alia, I don't know if you can export/save the motion path and import it into ShowCase, which means that you're animation work in Alias may all be for nothing.
If you know how to animate in ShowCase, then I'd advise you animate your model there.
Hope that helps.