With Canva's frame functionality, you can only frame one item at a time, which can be very limiting. So, I've created these "reverse-mask" cutout frames. Rather than dropping an item into the frame like you do with Canva's frames, you'll just overlap your whole multi-element scene with one of my cutout frames. It creates a "window" into the scene.
 
These are in vector format so the color can be changed and they can be scaled to any size. Each frame is in its own SVG file.
 
HOW TO USE:
Unzip the file on your computer.
Go into a Canva project
Click Uploads on the left side of your screen
Click Upload Files
Find the folder that you unzipped in Step 1
Select everything in the folder (you should be able to click on one of the SVG files, then do Cmd/Ctrl + A to select ALL)
Click Open
 
Now, you can grab a frame from your uploads, and drop it into your project. Resize to fit. If any parts still need to be covered on the edges, you can create a rectangle (press the letter R on your keyboard) to fill it in.
 
You can change the color of the frame from the color menu across the top of the screen.