Question about visitor visa application

[bear]

Since I saw a sample of invitation letter which was posted in CFC by Lucy Zhang late last year, it looks like that I can apply for the vistor visa for my parent in Detroit in stead of BeiJing. Is that true? Anyone has this experience can confirm it, and please advice is it possible to inquire the detail with the Consulate General of Canada in Detroit? and How?

Thanks a lot!