Morning Adam
Hope you are travelling well!
Thanks for getting in touch.
So I probably should start with a disclaimer - I don’t use Canva for developing anything cinematic, if I can use that term here, but really just stock footage. In other words, just bits and bobs.
If you are chasing something Orwell, or Kubrick, then yeah…hard no.

Lol.
As for simple, stock footage though - absolutely yes!
If you need some rain drops on a leaf? Done. If you need kids playing in the park on a sunny day? Done. Canva AI excels at the simple, vanilla shot that a student might use in say a social media video, a montage etc and so on.
This is what my advice is steered toward. If you are chasing simple shots for free, then Canva is the best on the market. I wasn’t referring to cinema conventions. I just assumed we all knew what I was talking about…my fault.
Canva AI will not produce an “in-line” shot for a scene or sequence that sustains a visual look, consistent lighting etc and so on. It just doesn’t have the memory capacity to decode a prompt that long, and it doesn’t have the functionality to support continuity by uploading images.
In fact, pretty much no AI model out there can do that to the level of (your) satisfaction. Even paid stuff like Runway, with all its gimmicky promises, still fails in creating continuity for cinematic shots that matches the sequence perfectly. The hardware requirements (such as memory) is just not there yet.
You can see this problem in ChatGPT where conversations are getting too long, and the AI output starts to “forget” things you had in your original prompt - this is the hardware problem. All AI models suffer the same thing.
So what does this mean?
Use Canva if you need free, good quality stock footage. The generic type of filler. If you want something cinematic, then you’ll just have to shoot it yourself I’m afraid.
My prompting…
Because I use Canva for simple shots, I tend to only type in what I need in terms of basics and I defer to the model to fill in the gaps. For example: Long shot of dog running along in the park on a sunny day. There are two reasons for this simplicity: 1) I don’t have the time to dig into the prompt and 2) It’s just a simple shot I’m chasing, so I can’t be bothered.

Lol.
In essence though, your prompt will reflect your needs for the project really. When I was discovering this endless supply of stock footage, I needed some nature shots for a video the School Admin requested. So I grabbed some “rain on a house gutter” and some “rain on a leaf” type shots. They came out perfect (in my opinion) and well, it worked. This impressed me so I wanted to share it.
And that’s basically my workflow for Canva.
If I missed something in your questions, please let me know.
Here are two video samples I created in Canva using AI:
Link (Beach Waves)
Link (Rain on Gutter)
Hope that helps.
Chat soon.