I am not familiar with Bokeh but I have used Django and Flask. They represent two different ends of the framework spectrum. Flask is a minimalist framework with URL mapping and html templating system. It has lots of additional addon modules to be mixed and matched as you need. Select Flask if minimal dependency and maximum flexibility is needed.
Django is a much more full feature framework that includes an Object Relational Mapper (ORM) to map SQL data models to views. It has a lot of scaffolding that meets common needs of web apps.
They are both excellent, high quality, well-supported frameworks that take very different approaches. I tend to favor Flask for little projects with simple needs. If I want to get user management, permissions, and data model mapping I might use Django or other more fully functional framework. In general, I like the smaller granularity frameworks provided there are well-known and documented solutions for standard problems. I find the big frameworks good for rapid startup but often you pay the price later when your requirements split from the standard implementation. That said, a framework like Django will let you split from it's default implementation. Django reminds me a bit of Ruby on Rails or Grails in that it tries to solve so many problems that it becomes large and somewhat cumbersome.
In my current job I am using both Flask and Django Rest Framework for two different portions of our software systems. My advice to pick which one is to enumerate the functionality you will need around common use cases like login, user management, forms/templates, CSS, CRM, URL mapping, data models. Then look at the features of each candidate framework. Additionally you should examine the style or approach each takes. You might find friction with one approach and your own approach which leads you to favor a different one. Ideally you want a framework that works the way you think, or at least one that is not contrary to your thinking. This is partially why I favor the minimalist solutions as they tend to create the least friction. But the reduction in friction often comes at the cost of needing more code written to achieve basic needs. Another consideration is the community and how well supported the frameworks are.
If you Google Flask vs Django or similar, there are a lot of blogs on this subject. Here's one example:
Django Vs Flask Vs Pyramid