The bear is almost as big as she is. Possibly bigger, because Alicia is tiny-sized. The cake is lined with candles that are magic and not real fire that would actually, you know, burn Alicia's house down, because he's pretty sure she would hate that and it's charmed so that a miniature game of Quidditch is being played just over it.
There is no note attached to any of this.
[For convenience sake, I'm saying that either the magical parts were set up beforehand and he just brought them out now or he got one of the people with borrowed HP powers to help him with this, so if your character got HP magic for the power swap plot and wants to volunteer to help a brother out, let me know, because I could just use Ginny, but it's more fun if I can involve someone else!]