Hi Ashleedolan ! Tag-teaming with my partner Peyton on this one :)
You are absolutely correct about the User Update approach. Unfortunately, it's not possible to split users based on the Canvas Entry Property (the Braze community is looking forward to this becoming a feature one day), so the solution would be to log the Entry Property as a Custom Attribute, then you can split the users using the Audience Path afterwards.
We actually have a Youtube video on how to do exactly this: check it out here!
It also sounds like you'll be using some Liquid to create conditional logic based on what your GET request returns from your BE. The Connected Content approach is correct here. Also happy to take a look if you have some more details/examples!