Formal:
* Bonjour, Allison. (This is the most common and polite way to greet someone.)
Informal:
* Salut, Allison. (This is more casual and appropriate for friends or people you know well.)
* Coucou, Allison. (This is a very informal greeting, similar to "Hey" in English.)
You can also use "Bonjour" followed by "Allison" without a comma, but it is less common:
* Bonjour Allison
The choice of greeting depends on your relationship with Allison and the context of the interaction.