'Cannis' - Term used in seventeenth-century clothes manufacture

I believe the product is canvas.

For example, see: THE LIVING AGE VOLUME CXCV, Publisher, Littell, Son and Company, 1892, Contributors Eliakim Littell, Robert S. Littell, Making of America Project:

Transcribed:

Coarse linen was woven by the village weaver into harn for shirts and bed-coverlets. The latter was cannis or canvas (Lat. canabis, hemp). A similar sheet was laid down to receive the grain when it was being threshed, hence the Buchan proverb, "We can thres i' oor ain cannis".

That is, you've heard of cannabis, marijuana, and its relation to the plan hemp, a textile. The textile is canvas.