Final answer:
Dairy cattle make up a significant portion of the total number of cattle in Canada due to the high demand for milk in regions with large populations.
Step-by-step explanation:
The approximate percentage of dairy cattle in the total number of cattle in Canada is not provided in the given information. However, it is mentioned that dairy farming is nearly ubiquitous across the US, and regions with large populations create high demand for milk.
Since milk must be transported quickly to market, the map of milk production echoes the map of the population. Therefore, it can be inferred that dairy cattle make up a significant portion of the total number of cattle in Canada.