I did see that the open source Gutenprint project has the MG5100-series on its list of supported printers, but I don’t know of a current port of Gutenprint to macOS.
The official Gutenprint macOS page only supports macOS 10.2 through 10.14. According to it’s FAQ, macOS support was dropped in mid-2024 and hasn’t had a maintainer for several years before that.
One potential workaround, requiring a second computer, would be to install Linux on a cheap computer (a Raspberry Pi would probably be sufficient). Connect your PIXMA to that, configured to print via Gutenprint (which is supported on Linux), and configure CUPS to act as a print server. Then configure your Mac to use a generic color PostScript driver, sending its print jobs to that computer.
You won’t have the same high quality that the Canon drivers provide (so photos may not look quite right), but that may work.
You can probably use your old MBP (which you say can print) in that fashion as well. Configure it for printer sharing and see if your new Mac can send PostScript jobs to it.
One other thing. In your initial message, you wrote:
That is a truly ancient version of the driver.
According to the Canon download page, the most recent driver for macOS 10.7 through 10.13 is version 16.20.
Version 3.4 is likely a non-CUPS driver intended for old PowerPC builds of Mac OS X. That would explain why it requires Rosetta.
CUPS-based drivers (like the latest versions) may or may not include executable code. If they consist of only scripts and data files, they may work on a modern version of macOS, even if they are not supported. If they do have code, but that code is 64-bit (which is quite possible), then it may work on Apple Silicon via Rosetta 2.
Again, I’d say give it a try. The worst that can happen is that it won’t work.