You asked whether "Australian or NZ production"?. Entertainment One is a Canadian production company while the movie is described as an Australian war film.
As for the accent of the troops, the unit involved is the 1st Australian Tunnelling Company coordinating under direction from Canadian and British Army Engineers.
Watched this last night. An excellent film. I generally avoid WW1 trench war films as I feel there is little new to say, but this was different - lots of claustrophobic action underground and well acted and directed. Nice to see the Australians in action. A few cliches and predictabilities but generally excellent. I'd recommend it. Thanks to @Nathangun for finding it.