For those working in data or product, how are you solving the problem of connecting user data across tools?

We’ve got marketing attribution, CRM activity, billing data, and product usage all in different systems. We’re considering Fivetran + BigQuery + Looker, but I’d love to know what stacks or strategies others have used — especially if you're automating it at scale.

Bonus if you have advice on keeping the pipeline maintainable long-term.