Arthur Gannon's "Peace Carriers" were part of a procession in the Wellington Peace Celebrations in 1919, celebrating the end of the war and the signing of the armistice between the Allies and Germany.  More information on the Peace Celebrations can be found here, on the NZ History website.

In an article in the New Zealand Free Lance, published Wednesday, September 10, 1969, in an article entitled "Arthur Gannon's Peace Carriers", it states:

Arthur Gannon’s Peace Carriers wore one of the features of the recent Wellington Peace Celebrations procession. They made a fine display, comprising nine vehicles drawn by-twenty horses, all elaborately decorated, and from one of the lorries the above typical bulldog, robed in a Union Jack gazed intently down on the crowds. In addition to the above display Arthur Gannon who is a returned lieutenant of the Maori Pioneers N.Z.E.F., placed a number of Lorries and expresses at the free disposal of the Salvation Army, etc

More information on Arthur Gannon can be found here on the Auckland Museum website