Q: Product generates temporary XML in cannonical form but I need XML with attributes. Is it possible to create such XML in Region2XSLTReport?
A: Yes. In Region2XSLTReport you can apply two XSLTs. Use first XSLT to convert elements to parent element attributes and then second XSLT to do actual transformation. Here are examples of first XSLT
Q: Is it possible to create bar codes?
A: Yes, it's possible to generate bar codes inside XSLT or PL/SQL (User Guide chapter 2.6 Procedure ConvertBlob).
You can find some libraries and examples how to generate barcodes with XSLT. For example check Barcode4J.
Here is APEX and PL/SQL example: http://apex.oracle.com/pls/otn/f?p=31517:101
If you need just UPC barcode also SVG can be used.
For documentation see Docs & Samples.