The CASA Tier 2 for this kind of web app can be done through DAST - dynamic testing which does not require source code.
Mine - before they require now to go through Authorised Labs (which basically are doing the same tests as mine).
In any case you always have 2 steps, the first one is the testing of your app, you get a report with open items to fix/justify and then after validation you get the certification. Any any case, no certification process guarantees that you WILL get certified, however I can testify that Bubble platform is no blocker for CASA Tier 2 Assessment.