SJ0110 : Cann Office Hotel, Llangadfan Cann Office Hotel
It seems odd to say "'Cann' = can (of ale)" when the link provided says the name "is actually derived from 'Cae'n y ffos', meaning fortified or ditched enclosure, and an old earthwork belonging to a twelfth century motte and bailey is in the inn's back-garden. "
Other contributors seem to have picked up this explanation, some have other suggestions.
My Welsh dictionary includes:
cān -
n. song
can -
a white
n.m. flour
cann is not there at all but cannaid (white, bright, luminous) cannu (whiten, bleach) and cannwr (bleacher) suggest it would have something to do with white.
SJ0110 : Cann Office Hotel, Llangadfan SJ0110 : The Cann Office Hotel, Llangadfan SJ0110 : The Cann Office Hotel, Llangadfan SJ0110 : Cann Office Hotel SJ0110 : Sign for the Cann Office Hotel