Although a Canadian Red Ensign served as the national flag during WWI, it was not the version with the national coat of arms shown. That one did not become common until the 1920s. The 1917 version had a sort of oval crest containing several provincial coats of arms.
In many of the night scenes, the city is lit by streetlights and bright windows. At the time, Halifax was under strict blackout orders, meaning streets would have been dark.
The folding camera used for the family portrait is a type not made until the mid-30s. Nor in 1917 would there have been a self timer or a flash bulb. If the flash was supposed to have been done with flash powder(which was used at that time) it is unlikely an amateur would have it and it certainly could not have been set off by a self timer, even if one existed.
There is a scene at the railway station in which a rail car carries the old CNR logo (A maple leaf with a box inside it containing the words "Canadian National Railways"). The CNR was formed in 1923.
When the French captain and his crew are arrested, the Mountie determines that the captain is lying about being from Montreal by asking him who won last week's hockey game between Montreal and Toronto. When the captain guesses "Montreal", the Mountie draws his gun and says it was actually Detroit. This dialogue seems to be referring to the National Hockey League, which was formed the same year of the Halifax Explosion. Toronto and Montreal would have had NHL teams at that time, but Detroit didn't enter the league until 1926. (Although Detroit is known as an "Original Six" team, this actually refers to the six teams that comprised the NHL for several decades; the NHL was originally an all-Canadian league for back in 1917, there were no American hockey teams with the league.)
When the speech is being given in Boston, at the end of the movie, the city hall behind the big tree is actually the Halifax City Hall, not Boston's.
The town hall scenes are filmed in Grace United Church in Dartmouth. Visible is a brass plaque on the wall which recognizes the efforts of the congregation in the rebuilding of the church after the explosion - Grace United having been destroyed in the Halifax Explosion.