This happened a week ago, but I only just came across it.
I don't think anyone's taken responsibility, but it looks like ALF. Also from their site:
According to media reports, as many as 6,000 mink were released from cages early Saturday at a fur farm near Harcourt, a town on the east coast of Newfoundland.
The Harcourt Mink Farm (located 1 kilometre east of Ryders Brook Bridge, off of Route 232, on Trinity Bay) is owned by Jorn Mogensen, a Danish mink farmer who operates several fur farms and related businesses in the area.