My Canadian visitor's visa is expiring, when should i renew it?

[GeeO]

I have to renew my canadian visa as it is expiring on the 22nd of september and i plan to visit for canadian's thanksgiving in october. Now the issue is that the detroit office no longer does walk ins and so i have to mail in my passport and the minimum time is one month. So calculating one month from the time I want to visit would mean applying for my visitors visa before the old one expires.
Is this allowed? Or do I have to wait till my old one is expired before applying for a renewal?

 

[Safou]

apply for extension from within Canada..

 

[Creampop]

your american? what are you going to Detroit for? you don't need a visa to visit Canada... once you cross the border (going to Detroit) your visit is over you cross back ...if they let you in... otherwise do as Safou said as long as it is before 6 months from the date you entered (even without a stamp they know when you entered) you will have "implied" status until you receive a decision....