My experience with CDN dollars all over SE Asia is that it is a very minor currency and the premium or discount over the Int'l FX rate is very large over USD, Euro, Yen and RMB.

You will get it changed at major centers, but at what rate? In Toronto there are many money changing only storefront operations who have a very competitive CDN to US rate. When I do the math with my cost of US$ and the local US$ CDN$ rates I am always ahead going CDN>US>local.