Sorry, I don't know the precise cancellation date. Maybe it was cancelled because of financial reasons or a shift in the target audience. Try doing a search on popular entertainment websites for the accurate information.
Not at all. Shonen manga is a broad category, and while Shonen Jump is a well-known and significant publisher, there are numerous other publishers and online platforms that feature shonen manga. It's a diverse landscape with various options for fans to explore.
John Singleton isn't the host. Comics Unleashed has its own dedicated host and John Singleton isn't part of it. Maybe you got some misinformation or there was a confusion.