Good morning, @SeanKim ...
To my knowledge, neither option that you've asked about are possible within Canvas Studio...or the Canvas RCE (Rich Content Editor) for that matter. You cannot split a single video into two parts, and you cannot combine two separate videos into one file within Canvas Studio. Those are not functions of Canvas Studio at all. I am also not aware of any online tools that integrate into Canvas that would allow you do any of this. (I could be totally wrong, though, and I'd be interested in learning from others if there was such a thing.)
I'll also add that if you wanted to see this kind of functionality in Canvas Studio, you could certainly create an Idea here in the Community for people to evaluate. Here's a few documents for you to read over:
Community - Instructure Community (canvaslms.com) - Check out the section on "Ideas and Themes".
Sorry that I don't have better news for you, but I hope this helps to answer your question.