My girlfriend will get a green card in Canada next year. Should we get married before or after she gets the green card, so that it is more convenient for me to get the green card smoothly?

Of course, it is more convenient to get married first and then get a green card. It would be better if you apply for skilled migration, because Canada's immigration policy stipulates:

The application for general skilled immigrants is made by the whole family at the same time. As long as the main applicant is approved to immigrate, the whole family can immigrate with him. Family members here refer to spouses and unmarried children under 19. If the child is studying full-time (like a university), as long as he is unmarried, he can immigrate together even if he is over 19 years old. Because general skilled migration, Canada has an extremely important relationship with the application work, only occupations that meet the needs of the Canadian labor market issued by the Canadian Immigration Department are eligible to apply. Therefore, who is the main applicant of both husband and wife should be decided according to the occupation and other personal conditions of both husband and wife, and the main applicant is the most likely to be approved for immigration. As long as the main applicant's immigration application is approved, the whole family can accompany the immigrants. Who is the main applicant of both husband and wife should be determined according to their respective professional and other personal conditions. The spouse who is most likely to be approved for immigration is the main applicant. As long as the main applicant's immigration application is approved, the whole family can immigrate with him.

If not, you can only apply for visiting relatives or applying for family reunion immigration after the applicant has landed.