Comment by xiphophilos:
The fact that the company name is "Columbia Graphophone Company", introduced in 1913, shows that this can't be a 1910 release even though the song on the A side was recorded in 1910.
Per Ted Staunton: One of a series rushed out to satisfy patriotic fervour at the opening of World War I. Many regiments were formed in Canada to augment the British Army. The 'P' designation at the foot stands for 'Patriotic Series.'(
source)
For more examples, see
here.