I've bred & shown Cairns for over 30 years.
They are just like a Westie, but all the colours except white.
Here in the UK, Cairns & Westies were all one breed in the beginning, some coloured, some white, all Cairns. Then in the 1920s the Kennel Club allowed the white ones to be registered seperately as Westies.
Showing my Cairns, I meet lots of Westies at the terrier shows. Both have the same great little characters, full of life & fun.....it's always a case of "Look out world, here I come!"
Their coats are the same, it's just that the West Highlands are trimmed more than the Cairns.