When is a good time to buy currency? CAD --> EUR?

Personally, the best time is at the time of travel. There is no way to be able to accurately predict the ebb and flow of currency market fluctuations. The professional currency traders make a living out of it, but they also trade in vastly more currency than you will use on your trip. The best idea is to use your credit card wherever possible to get the best exchange rate (make sure to ask your bank about what their foreign transaction fees are). After that, just don't worry about it, since you are not a currency trader. Enjoy your trip!