As you know, eBackpack had built in tools to let you write on (annotate) certain kinds of documents. As you also know, it didn't always work well for every student.
Canvas takes a different approach. In Canvas, we don't have built in tools to annotate on documents, but canvas does make it easy to download documents to your device, use other apps (programs) to write on the documents and upload the document to turn it in to your teacher.
Teachers will usually provide a PDF document if they want you to write on the document. Here are some PDF annotation programs that you might want to try. Different people have different preferences and needs, and there are dozens of programs like these, so if you don't like these, search for a different "PDF Annotation Program".
For Microsoft Surface and Windows 10:
For iOS (iPads & iPhones):
For Android Devices:
If you have another program that you like, let me know and I'll add it to the list.