The steps depend on what transactions you are looking to be synced:
1. What all transactions should be synced from Hubspot to BC
2. What all transactions should be synced from BC to Hubspot
3. What master (Customer, Item, etc.) tables data would be exchanged in the integration and what will be the direction of sync?
Additionally,
1. Will it be a file exchange data sync? (Where a file is received in a folder and absorbed in BC)
2. Or will it be a direct API Integration? (Wherein BC will talk with Hubspot directly)
Also,
1. Is the customer okay to use Power Automate / Az. Logic App (in addition to BC)? These services do come with additional licenses/costs