Sage doesn't use SSRS.

Yes, I know but I want to customize it.

SSRS is a simple product.  What can't you figure out?

Yes - I've created many SSRS reports from the Sage database.  

Can I assume that you're familiar with SSRS and need assistance determining which tables to use?

I need to connect it to sage300 is it possible or not?

Yes, of course.

Yes, I am familiar with SSRS and from the database, I can manage to preview the report through the localhost but I need to preview through the sage screen. Is it possible?

No

Not without some customization and using a link referencing the report and the invoice as a URL embedded parameter.