* Canner: Someone who preserves food by canning it.
* Exceedingly: To a very great degree, extremely.
* Canny: Clever, shrewd, and astute.
So, "a canner exceedingly canny" means someone who is a very clever and shrewd food preserver. They likely know all the tricks of the trade, are resourceful in using their resources, and can get the most out of their canning efforts.
It's a playful way to describe someone who is both skilled at canning and intelligent in their approach.