listbox -vs- checkboxes implementation?

Hello - I have a custom entity. For each instance of the entity, the user should have the option of selecting a specific set of workflows he wants to associate with the entity. I can get a UI working for this, but I'm trying to think of the best backend design and UI implementation.

Since there will be a 1-to-1 relationship between the custom entity and w/f type, I could simply add the workflow options as fields on the entity.  Then, I could add checkboxes to the form for w/f selection for the entity. I think CRM would support this implementation ootb pretty easily.

However, from a general UI design perspective, it would be more appropriate to group these w/f options together in a multi-select listbox, since the data options are related. So what are my options for displaying these options in a listbox?  From a CRM perspective, is it going to be impractical to implement this solution as a listbox instead of checkboxes?