McLaren returned to Scotland from 1910 to 1914, to study architecture at the Edinburgh College, but found the drawing and painting were more suited for his talents. Soon after his return to Canada, McLaren enlisted in the 4th University Infantry when the First World War was declared in 1914. However, a bout of hepatitis at training camp near Valcartier, Quebec prevented him from being posted to the front lines. McLaren re-enlisted in Toronto in September 1915.