A link to Transport Canada's website, with all of the information presented on this page is here. Thanks to Suzie T for the link! From there, you can spend all day investigating the remainder of their website.
Almost all signals in Canada pre-1990 are single-lens searchlight signals and normally you'd find signals arranged as one, two or three aspects (heads) mounted on a single mast. CROR Signals are designed in principle to display speed information only - how fast the engineer may proceed now and approaching the next signal. More complex signals (e.g. three heads) can display a wider variety of speeds. On a high-speed mainline, a single-head signal is sufficient to display all necessary speed information (i.e. full speed or prepare to stop) however where switches are involved such as a crossover to another line, two or more heads may be required to display the fact that the engineer may have to slow to medium or limited speed to pass the switches before continuing.