To be clear, the Fed interest rate hike itself is not "good news" for the Canadian dollar. Increased oil prices are. To the extent the Fed's announcement was positive for the dollar, it is that the reading of the "tea leaves" in the Fed statement around the increase led traders to conclude they had over-sold the Canadian dollar because they now believe US interest rates will rise more slowly than they believed they would the day before. That is they are guessing that their previous guess on interests rates was a little off. The luckiest guesser will make the most money.