So, I did a first trim of the canopy with a cutting disc in the die grinder. This is mostly just to gain experince and see how to do it. It works better if you feed against the rotation of the disc. Otherwise, the detritis gets caught in the groove you just cut. Also, it takes about 3-4 passes to get all the way through. Other than that, it was not particularly challenging.

Trimmed off about an inch.

I also tried this oscillating multitool. It didn't work well for me at all. The kerf would just load up with debris and cutting would stop. I checked and this model has bout 2.5 degrees of oscillation which isn't enough for the chips to come clear of the material given it's thickness. Perhaps a tool with more oscillating angle would work better? Unknown...I'm going to stick with the die grinder and cutting disc.