Well Mike, it looks that not many Canadian members here know much about this regiment
Some speculations:
The 26th and 27th started life in 1910. The 28th did so in 2011. The 30th and 31st came from British Columbia into the line in 1912. My speculation: the 29th dates from 1911/12.
The 18th Mounted Rifles is from 1908 and the starting dates of the regiments "around" it confirm that that is within the range to be expected. As the 18th was not disbanded as far as I know, how could it's place be taken by an 18th Canadian Light Horse after 1912????
PS, I am trying to keep this thread alive in the hope that someone with knowledge might stumble into it. I can be nasty.