As to the original topic, why Canada doesn‘t have marines, I dunno... I imagine we don‘t have a modern marine force because of all the reasons others have mentioned: No troop carrying ability, and it‘s really duplicated anyway by our infantry.
Probably historically, we never needed a marine force.
There would have been a small number of Royal Marines in Canada that went where ever the Royal Navy went, but this probably ended not long after the War of 1812. In those days, a wooden frigate WAS a troop-ship, quite often. It was the single most powerful, mobile way of implementing foreign policy. The Brits never built that many ships here, and the naval activities were really kept to the East Coast (until much later on).
In the interior, we needed a good militia, backed by British regulars, when they could be spared from the war in France. The original purpose of the marines was to provide an infantry force capable of protecting the ship and it‘s crew, and was very limited in it‘s offensive role. The whole ship‘s crew would often be used for offense, for example boarding a ship, or attacking a town or fort from the water. The infantry was used for more serious land-based maneuvers, and could be ferried if possible, but not often used in a marine role.
