Can I pass link data to my Journey banner, so that when the app opens using the journey banner, the SDK can read that data?

Yes, this is possible, you can configure the link data and pass it to the link in the banner CTA using the setBranchViewData() function from the web SDK, please refer to the below link for more information on the same:

https://help.branch.io/developers-hub/docs/web-advanced-features#create-journeys-banner