Some tips for you:
1) Before uploading programatically, you need to convert excel files to Google Sheets format (you can re-export them to .xlsx).
2) For this your application need reference of Drive_API_Dll(s) which are available if you have Google Drive API and Google Drive SDK packages installed in your Visual Studio.
3) Most important thing you need to follow while uploading files to Google Drive programatically is you must have to go through (i.e. implement) Google API authorization.
4) You can do this in C# by using the Google Drive API Client Library for .NET.[You can download it from here: "https://developers.google.com/api-client-library/dotnet/apis/drive/v2"].
5) Follow this code snippet.
Hope it helps.