How do i become a commercial seafarer (Canada/Quebec)

I'm looking to make a career switch and have been interested in becoming a seafarer. Only thing is i'm not certain on how to join, so here's my questions.

• What are the requirement in order to become an ordinary seamen?

• While being a ordinary seamen, is there possibility of advancing in different type of field (cooking, engineering, etc) as some sort of bridge between seamen and these skilled profession and does it required external studies or you are taught while on board of the ship?

I understand that these questions are asked often but i couldn't find the answers i was looking for.