I'd be a bit hesitant at this point to transition a large amount of money from CAD to USD just because of the weakness of the CAD versus the USD. I buy USD every week with my weekly contributions, which allows me to smooth out currency fluctuations. But I also realize right now I am buying USD at a historically weak time. Typically, the dollar tends to hover around the $0.75~ mark. We're now sitting at $0.72.
If you're looking to transition out of CAD and into USD, you could do it over a longer duration of time to smooth out currency risk. It is a difficult decision to make, and one that is solely dependent on the investor.