My list may be out of date. The legal volunteers at Project Gutenberg will help you with copyright checking if you supply them with photocopies of the title page and the copyright page. As a rule of thumb, works published before 1922 will usually be out of copyright. Many later works are also out of copyright, and some works published before 1922 are still in copyright in some places. So check the copyright on the specific work first.
Legal jurisdictions are numerous, and greed is abundant.
Do the scanning and proofreading work. This is very hard work. Maybe you can find others to help you. At the very least, please tell me about your project. Publish a flat text file through Project Gutenberg.