In a large bowl, combine the berries, turbinado sugar and orange liqueur. Toss gently to coat and marinate in the refrigerator for at least 1 hour and up to overnight.
When you're ready to assemble the trifle (don't assemble it more than 8 hours before you want to eat it), slice the domed top of the cake off and discard (or save it to snack on).
Slice the remaining cake into two equal layers (they should each be about a half-inch thick). If your cake is a little bit too large to fit inside of your trifle dish, cut a small wedge out of each layer and then fold the cut sides together to make it fit.