Final answer:
Considering similar trends in comparable advanced economies, the educational attainment of Canadians has most likely 'C. increased dramatically' over the last few decades.
Step-by-step explanation:
The question pertains to the trend in educational attainment of Canadians over the last few decades. Drawing on understanding from the provided context regarding the United States, a similar developed economy, we can infer that like the US, education levels in other advanced economies such as Canada have likely increased. While the US-specific data points to a significant rise in the population with high school and college degrees, a direct answer based on the options provided can be formed.
Given that human capital deepening in the US has involved a substantial increase in the educational levels, with over 80% of US adults having graduated from a high school by the twenty-first century, it is reasonable to conclude that the educational attainment in Canada would have followed a similar trend. Therefore, based on the available information and trends in comparable economies, the correct choice relating to Canadian educational attainment would most closely be 'C. increased dramatically'.