A ha! Tracing back from that information, it seems that Hjalmar and Valgerdur Hjalmarsson started going by the names Charles and Bertha Hillman after they were married. Knowing that, without much difficulty I've now been able to gather a whole lot of information about them and their descendants. Interesting information about Oscar too. He seems to have been involved in many of the key battles for Canada in WWI.
Thank you again!