There are two rates which determine what you pay in canada using USD. The first is the official exchange rate which changes sometimes daily and at least every two or three days. The second is the BANK FEE which some banks charge to handle your transactions in USD.
Most credit cards charge you 3%-4% transaction fees for use in Canada, but Citi doesn't. There may be others who don't, too.
I have to go up there on business often
(I hate it) and what works best for me is to buy Canadian dollars at my bank here, when the official exchange rate is favorable to us. Then I end up driving there with several hundred Canadian dollars and a few hundred USD and hope the exchange rate changes while i'm there 
. Another option is to buy traveller's cheques at AAA but I have no experience with that in Canada.If you travel in Montreal be aware that their constitution requires them to be a bi-lingual nation, with everything written in both English and french. But not a single parking sign (and few direction signs) in the city are in English, the parking scheme changes BY THE HOUR and is different every 200ft down the same side of the street, and parking tickets cost $87 USD.
They are an evil, dishonest people there and "some" of their cops will intentionally write you a ticket before the parking time expires and lie about what time they found you. You can park legally in a 3-house stretch of a street and be required to move your car either to the other side of the street or 3-4 houses farther down your own side of the street in another 4hrs, in order to be in compliance with the constantly rotating parking hours. I've come out to my car 1/2hr before I was required to move it (0630) and found a ticket on my windscreen marked for 40 minutes later. They are a corrupt bunch of thieves up there and they love rich foreigners. Wish we had an appropriate Smilie to indicate how I feel about them, but this will have to do for now: 
Their parking meter system was not familiar to me before I saw it in Montreal, but I was dismayed to recently see it being used in Syracuse during a brief visit there. Each space along the curb has an alpha-numeric designator painted on the curb or on the wall of the bldg it's in front of (how about THAT? The government themselves paint graffiti on your private bldgs!). "Somewhere" along your street is an automated parking pass kiosk about the size of R2-D2. Each kiosk services about 10-20 parking spaces on that side of the road. It can be anywhere within those 10-20 spaces. It's up to you to find it. (HINT: it's ALWAYS in the opposite direction from your destination).
You put CANADIAN coins in it for how long you want to park, type in the letter and number of your parking space (you'd better get it right) and it dispenses a little ticket showing the expiration time, which you then must take BACK to your car and leave face-up on your dashboard. I can't tell you how much fun that is in the hard rain while your family waits on the sidewalk for you to return.
Oh, canada.
The only advantage to visiting there is that the city streets are always spotless (street cleaners run constantly), which is their excuse for hammering you $87 for parking tickets, and that Canada is exempt from the Cuban embargo. You can buy cuban cigars up there and most visitors do.