I'm sorry I can't help you about choosing plant material that would grow best in Florida (I'm from the midwest); but, interestingly enough I found something on the web in regards to using bougainvillea in topiary! A hotel in Thailand has an elephant topiary of bougainvillea, but I could not find a photo of it. Don't know the variety or any particulars about it. Also, does this plant have sharp spines? Didn't know that either. So, I guess the only thing I can contribute to your question is that, yes, bougainvillea can be used in topiary.

In your area, do you grow this as a shrub in the garden year round? Or in pots and bring them in during a cold season?