The in-camera setting of AdobeRGB only affects the camera JPGs, and once the images, JPGs or raws, are inside of LR the working colorspace is specific to LR and cannot be changed and has nothing to do with the camera setting of AdobeRGB even if you’re processing JPGs from the camera.
To print properly from any program, you either need to have the program converting to the printer’s colorspace using a printer or printer-paper profile from the printer manufacturer and have the printer set to not use color management, or you need to have LR printing to the printer in a standard colorspace, perhaps sRGB, and then the printer set to expect that colorspace.
I would guess you have the printer set to Auto which probably works the best with sRGB output, and then LR is sending AdobeRGB output which will be greener and less saturated, perhaps.
Do you have printer profiles that LR can use to print to the printer?
Have you found where in the printer driver (settings) to turn off color-management?
I have the Pixma Pro-100. Not as advanced as yours, I realize. But I believe you will get better results if you acquire profiles for the paper you are using and work with the paper profiles rather than trying to use Adobe RGB. I have profiles for every paper that I use and get excellent results from the printer.
Thank-you ssprengel and JimHess for your replies. Let me investigate.