For your question, it is impossible to get 6-month or 12-month visa to enter and stay in Vietnam. For Canadian citizens, you can just use Visa On Arrival with the maximum length of stay is 3 months. However, it is possible to expand to stay longer with this kind of visa, so you can consider to choose and apply for it. 

This below price table is applicable for Visa On Arrival with tourism purpose:

E-visa is also a kind of online visa, but it is just accepted to stay in Vietnam for not more than 30 days. Visa On Arrival allows Canadian passport holders to be able to stay for not more than 3 months. Then, you can totally extend your next 3-month visa.

Take note: 

With Visa On Arrival, you can just enter Vietnam through 6 international airports. Any other border gates or seaports are not accepted to enter with this kind of visa.