Any recommendations for a guide for a 2 night/3 day Colca Canyon trek?
You are going to LOVE the Colca Canyon!
I don't actually know any specific tour companies that only operate in the region (I booked my last trip with a full Peru itinerary).
However, most lodges in the area will arrange for hiking and camping trips so it may be a good idea to go direct and local -- will also save you money if you book for stay+hiking.
I can def recommend the Killawasi Lodge in Yanque. I discovered it by chance and it is my favourite place to stay in Peru. It's community run, small, simple but with very modern ammenities and great service. The lodge is located outside the main tourist stop so hiking is much more secluded, stunning and you will walk among local farms and friendly residents. I was there in April during the potato harvest and got such an amazing collection of pictures!
Quite jealous you are heading off to such a stunning location ;)