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I think that it's generally understood that bots read page code, they don't "do" page code like the browser does, so the canonical is read, regardless of the other code on the page.
This wouldn't be the case for 301's that trigger server side, the bot would then never reach the page to read the canonical.
HTH
You don't have to duplicate it if you're just trying to tag the product title, though the FAQ says you should use Schema for more details about your product to get the most benefit from Schema.
The end goal should be to leverage as much benefit from the pages as you can for your existing business direction without confusing or tricking your visitors. The approach to your issue might depend on what type of content this is.
For example, if your content consists of well written articles that are relevant to the visitors that are still reaching these pages, you might try and leverage that traffic through some well placed call-outs or advertisements for your new service/products/blog. The visitor gets the information they searched for, and you have a small potential to get some benefit from your past work.
If your content consists of eCommerce pages for outdated or discontinued products and you have similar or replacement products, 301 these pages to your newer relevant product. Consider explaining to the user why they have been sent to a page containing a different product and that the new product is the replacement for the older model.
If you don't have replacement products, and your pages aren't useful content, then you have to ask yourself why you care about the pages getting a lot of traffic. You are hesitant to cut it off because hey, people are visiting the pages and that helps your site overall right? Not if it's bringing your site traffic that doesn't convert.
If you're trying to optimize your site for a completely new set of terms, the old pages shouldn't hurt you too much as long as you are handling them correctly. Google doesn't like it when you try to trick it into thinking that a page/site is about subjects that it's not really about.
You don't mention anything about the new business but I am curious, if it is such a different direction, why not a new website altogether?