After the First World War, the Canadian Pacific realized that a significantly more powerful Pacific was needed for the new, six-axle heavyweight passenger cars. Chief engineer William H. Winterrowd then developed the class G3 with a driving wheel diameter of 75 inches, which was intended for the flatter routes. A total of 26 examples of the G3a, b and c variants, which were almost identical in construction, were completed by 1923.

In 1926, 25 examples of the G3d followed, the most important innovation of which was a boiler made of nickel steel. This allowed the boiler pressure to be increased from 200 psi (13.8 bars) to 250 psi (17.2 bars). Although the cylinders were made smaller at the same time, the starting tractive effort could be increased.

Twelve years later, the 27 examples of the G3e and f followed, which in turn benefited from new advances in boiler construction and now had a boiler pressure of 275 psi (19 bars). The cylinder diameter was reduced again, while the starting tractive effort remained about the same. The G3g, h and j reached the largest number with 93, which only followed in the forties and were almost identical to the series e and f in terms of the engine. However, they had a boiler with fewer tubes and were used with smaller tenders. They were real multi-purpose locomotives and were also used in front of freight trains.

Although it was precisely the later variants that came up at a time when other railways had already switched to 4-6-4 or 4-8-4, they were relatively strong compared to other Pacifics and had a better ratio of adhesive to service weight than other locomotives and had less of a tendency to slip. The period of use ended in 1959, when there were already enough diesel locomotives for their area of operation. Today only number 2317 still exists, which belongs to class G3c.