This documentation from Google Cloud could help you to achieve what you want to do:
"This tutorial shows you how to create and deploy a pipeline that continuously replicates changed data from a Microsoft SQL Server database to a BigQuery table."
This other page shows another alternative to connect SQL Server with BigQuery.
But consider that the tutorial from Google Cloud relies on the CDC (Change Data Capture) feature, which
"is supported in the Developer and Enterprise Editions of SQL Server up to and including SQL Server 2016 RTM."
As stated on Microsoft’s site; MS SQL Server 2014, which is the one that you’re using, has reached its End of Life, and is beyond support.