In fact, Frank Mitchell has written to me with some further
insights. I quote Frank:
Interesting photo of what appears to be a 'very new' A2
double heading with a 'Pheonix AA'
A2 798 was brand new in December 1910, your 'Wiki'
reference to the AA's lasting until c.1930 is a little late,
they were mostly gone by 1923-25, certainly from Main Line
duty as depicted here. Only 4 lasted a little beyond
then.
A2 798 was renumbered in 1923 to A2 842 during a
reclassification, so this photo has to be early in its
career and pre WW 1 - I suspect, she looks very resplendant
in the "Canadian Red" livery of Railway Commissioners
Chairman Thomas Tait.
Tait came from the Canadian Pacific Railway in 1903, and
bought his 'colour code' with him!